I did not test as extensively but this is still a bug in Plasma 5.25.1, though with slightly different and more consistent behaviour. Now, the system seems to *always* lock up (tested three times) after searching and closing the Overview effect.

STEPS TO REPRODUCE
1. Activate Overview effect
2. Type something into the search bar
3. Close Overview effect
4. System locks up

When testing this again I can confirm it happens every time I search and close the Overview effect. One thing I did notice in these further tests is that the animation for bringing the windows back into focus does not ever actually finish. There are still some pixels along the sides of  the window where you can see it has not zoomed in the full way again, and also my scaled display is still blurry from having the effect activated as described in Bug 448567.

I cannot reproduce, never had it crash on me because of Overview. 
Can you run "journalctl -fe > ~/journal.txt" in the terminal, then cause the system crash and after the reboot, could you post the file "~/journal.txt" here?

Niklas, when requesting information, feel free to kick the bug into NEEDSINFO WAITINGFORINFO status. Thanks for the help with bug triaging!

Created attachment 150983 [details]
System Lockup Journal

Hi, thanks for the reply! I ran the command and then performed the steps to reproduce the crash. The file should be attached as a plain text file to the issue. I replaced my username with "/user/" but apart from that the file is untouched by me.

Due to the nature of the bug I had to press the restart button on my computer, but I let the machine sit frozen for about 10 seconds or so to hopefully let the file populate with any and all relevant output. If I need to run it again and wait longer to get more info, I can run it again.

For clarity, the steps to reproduce this for me is to simply activate the Overview effect (keyboard shortcut or screen edge, doesn't matter), type something in the search field, then close the Overview effect. Very briefly before the effect fully finishes, the system locks up. I can tell it's just before the effect finishes because the windows on my scaled display are still slightly blurry as described in another bug, and there is still a tiny line of pixels at the side of the screen just before the window finishes animating back to its full size and position. Hopefully this is clear enough! I'll also update my system information below as I have since upgraded Plasma versions and the problem still persists:

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 5.18.14-zen1-1-zen
KDE Plasma Version: 5.25.3
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.5

ADDITIONAL INFORMATION
- I am using the Zen kernel but briefly I switched back to the standard Arch kernel and still had the problem
- Have not tested X11 on my desktop
- This does not affect my Steam Deck (runs Plasma 5.23.5 X11 on a custom kernel)
- This does not affect my laptop (runs the same Arch as my desktop with the same kernel, Plasma version, and also runs Wayland)

Does this also happen with the Presentwindows effect (Default shortcut: Ctrl + F8)? I would not expect it to, but that way we can narrow down the bug. If it doesn't crash, then what about executing "balooctl enable"? Does this crash your system after a little while (under 1 minute)?

Present Windows didn't cause any crash, and I was unable to run that command. It said "File Indexer already running". I'm not sure which process for baloo (if any) are safe to close, or if there is a proper command to stop and restart the file indexer.

If you go to System Settings > Search > File Search > uncheck "enable file search", then does Overview still crash the system?

The system still locked up even after disabling file search. At first, the Overview effect closed and I was able to use my system for a few seconds, and then it locked up again. I tried this a few more times and each time was the same: The Overview effect closed and I could use my PC for a few seconds. I tested to see if it was some specific action that caused the lockup afterwards but even if I don't touch anything the system locks up after a few seconds. I have seconds enabled in my digital clock on my panel so when that freezes it gives a good indication of when its frozen, and it takes about 2-4 seconds.

I wanted to make note and reiterate something: I got a warning when I unchecked this, saying it will disable file search in KRunner too. I can search for files just fine without any lockups from KRunner, which I just briefly mentioned in the opening part of this issue. I search for files with with KRunner every so often and I haven't had any issues with it.

If your disk isn't faulty (hardware-wise, use any disk utility to check that) then I'm out of ideas. I'll leave this up to someone with more experience. 
For anyone trying to troubleshoot this, this issue is that KWin_Wayland crashes with SIGSEGV (=Signal 11) right after having started KRunner provider for baloo file indexer. The relevant lines from the journal are: 

Jul 29 17:42:58 endeavour dbus-daemon[826]: [sessionuid=1000 pid=826] Activating via systemd: service name='org.kde.runners.baloo' unit='plasma-baloorunner.service' requested by ':1.6' (uid=1000 pid=852 comm="/usr/bin/kwin_wayland --wayland-fd 7 --socket wayl")
Jul 29 17:42:58 endeavour systemd[811]: Starting KRunner provider for baloo file indexer...
Jul 29 17:42:58 endeavour dbus-daemon[826]: [session uid=1000 pid=826] Successfully activated service 'org.kde.runners.baloo'
Jul 29 17:42:58 endeavour systemd[811]: Started KRunner provider for baloo file indexer.
Jul 29 17:43:01 endeavour audit[852]: ANOM_ABEND auid=1000 uid=1000 gid=1000 ses=3 pid=852 comm="GlobalQueue[22]" exe="/usr/bin/kwin_wayland" sig=11 res=1
Jul 29 17:43:01 endeavour kernel: traps: GlobalQueue[22][2373] general protection fault ip:7f46bcef7346 sp:7f45ecff8770 error:0 in libQt5Core.so.5.15.5[7f46bcc9f000+2c8000]
Jul 29 17:43:01 endeavour kernel: audit: type=1701 audit(1659112981.368:102): auid=1000 uid=1000 gid=1000 ses=3 pid=852 comm="GlobalQueue[22]" exe="/usr/bin/kwin_wayland" sig=11 res=1
Jul 29 17:43:01 endeavour systemd[1]: Created slice Slice /system/systemd-coredump.
Jul 29 17:43:01 endeavour audit: BPF prog-id=25 op=LOAD
Jul 29 17:43:01 endeavour audit: BPF prog-id=26 op=LOAD
Jul 29 17:43:01 endeavour audit: BPF prog-id=27 op=LOAD
Jul 29 17:43:01 endeavour kernel: audit: type=1334 audit(1659112981.381:103): prog-id=25 op=LOAD
Jul 29 17:43:01 endeavour kernel: audit: type=1334 audit(1659112981.381:104): prog-id=26 op=LOAD
Jul 29 17:43:01 endeavour kernel: audit: type=1334 audit(1659112981.381:105): prog-id=27 op=LOAD
Jul 29 17:43:01 endeavour audit[1]: SERVICE_START pid=1 uid=0 auid=4294967295 ses=4294967295 msg='unit=systemd-coredump@0-2397-0 comm="systemd" exe="/usr/lib/systemd/systemd" hostname=? addr=? terminal=? res=success'
Jul 29 17:43:01 endeavour systemd[1]: Started Process Core Dump (PID 2397/UID 0).
Jul 29 17:43:01 endeavour kernel: audit: type=1130 audit(1659112981.382:106): pid=1 uid=0 auid=4294
[ This is the last line of the journal ]

Thanks for the help, sorry we didn't get anywhere but I appreciate all of your time regardless!

I don't think any of my drives are faulty though I will investigate and check, I do have a nearly 7 year old storage HDD in my PC but KRunner doesn't crash my system when I activate and search with it using Alt+Space, it's only in the Overview effect that it crashes. Also, even if that drive isn't mounted, the Overview effect still crashes my system. My other 4 drives are all SSDs and all only a few years old, I run games off them without any problems so I don't think they're faulty either. But it's a bit strange that my system only crashes with the Overview effect search box.

If there's any "preferred" way of diagnosing drives/getting drive health info to post for additional debugging, I'm happy to post that.

Occasionally I have been able to produce slightly different behaviour and I can do this on my PC with Plasma 5.25 and the 5.26 Beta, and on my laptop with 5.25. Both of these machines are running Arch Linux with the Linux Zen kernel, however I was able to reproduce it on my desktop before on 5.25 with the standard kernel.

If I type a math operation into the search bar on my desktop or my laptop, *occasionally* and *randomly* Plasmashell will die and restart itself. However, panels are unusable, they show the vertical or horizontal "stretch" mouse cursor mode. Which one it shows seems random as you move across the panel. To fix this you have to reboot.

When this happens, panel layout is preserved but wallpaper order is not. This is fine on my single display laptop but on my multi-monitor desktop this was a problem.

I have not been able to reproduce the system lockup on my laptop, but I can still reproduce it on my desktop on 5.25 and 5.26 Beta.

In the time following this report I experience intermittent and random system lockups during general system use, maybe two or three times a week, but potentially unrelated to this issue. The SMART status within Plasma says the disks are working as expected but if there is any other way I could check disk health please let me know.

Also on the subject of disk health, I'd just once again like to reiterate that this is ONLY a problem with the Overview effect search box. KRunner still works fine when searching for files.

This is still affecting me in Plasma 5.26.0, however the behaviour has changed slightly it seems like.

The first time I tested this again today, a few seconds after the lockup, Plasma restarted itself. The screen went black, then my wallpapers showed up, then my panels. So I tried entering some text into the search box again, and Plasma froze *with the Overview effect open* - Previously, it would only freeze when the Overview effect closed.

I restarted my machine and tested three more times, but I could not reproduce Plasma restarting itself. I guess Plasma restarting itself was a fluke, but I'll be testing into the future and I'll see if I can reproduce that behaviour again.

So the lockup still occurs, and KRunner is still fine, but now the lockup can occur whilst still in the Overview effect.

I wonder if this is the same as / related to Bug 448825 ?

Almost certainly.

Can you re-open this and un-mark it as a duplicate if you still experience the issue in Plasma 5.27, once it's released?

*** This bug has been marked as a duplicate of bug 448825 ***

Fingers crossed I won't run into it, but I'll keep this issue in the back of my mind and re-open it if I still have the problem :-) I run Arch (btw) so I'll be able to test with 5.27 fairly soon after release.