SUMMARY
When searching for an application in Overview, the results appear considerably slower than when searching with KRunner. Other PlasmaSearch entries (e.g. calculator result) are fast as usual. On my system, that has a rather large number of .desktop file entries, I have to wait a good 3 seconds (!) for the results to appear, with KRunner they are instant. While on clean installations, the wait time is maybe 0.5 seconds but this is still considerably more than KRunner's instant results. 

STEPS TO REPRODUCE
1. Pick any distribution with a recent version of KDE Plasma (I tested Arch, Kubuntu, Kali, KDE Neon). X11 and Wayland are both affected.
2. Activate the Overview effect
3. Search for an app that is not currently open

OBSERVED RESULT
There is always at least a slight delay before the results appear. On a cluttered system this delay quickly adds up, although it is present on clean systems too.
When it's especially slow (e.g. on my main system), the results will disappear with every keystroke

EXPECTED RESULT
The results appear just as fast as they would in KRunner (effectively immediately). This was the case for a long time. I cannot verify exactly when but an ISO I have from January 2024 works as expected (and faster than any current installation of KDE)

WHAT I HAVE TRIED SO FAR / MORE INFO:
- it does NOT appear to be affected by disk speed (tested with a ramdisk)
- it does appear to be affected by the number of .desktop files