SUMMARY
I am using KDE Plasma with Wayland on Arch Linux. I have a weird problem when the screen turns off due to inactivity. I have a Samsung Odyssey G65B monitor running in 2560x1440 resolution and 240Hz refresh rate. When I let the screen turn off due to inactivity, the monitor tells me it doesn't detect a signal, so it will go to standby mode in 60 seconds, which is normal. After it goes to standby mode, I shake the mouse to wake the system up. The screen flashes, which it usually does when being turned on or off, and I also hear KDE system sounds. However, instead of turning on, the screen tells me it can't detect a signal, and it goes back to standby mode. Shaking the mouse more causes more system sounds to play, but the screen won't wake up. I know the system does wake up, since I can blindly type my password to enter the desktop, and the keyboard lights up since its drivers take over. I can also blindly press a shortcut to open a terminal and type a command like `sudo reboot now`, and the system reboots. After reboot, everything is normal again. So the system does wake up and the desktop session works, but the screen doesn't pick up the signal.

There are some weird conditions and consequences of this problem, which I am not able to understand.
* The problem only happens on Wayland. If I switch to X11 and let the screen turn off and then wake it up, everything works fine. The screen wakes up, and I see the login screen.
* The problem only happens on 240Hz. If I change the screen refresh rate to 120Hz or 60Hz, there is no problem. The screen wakes up, and I see the login screen.
* Turning the monitor off and on usually doesn't fix anything, but there was one time it did make the screen wake up. I am not able to reproduce it consistently, though.
* If I press Ctrl+Alt+F3 to go to a virtual console, the screen wakes up and goes to the virtual console. Pressing Ctrl+Alt+F1 after that to return to the desktop session fixes the problem, and I see the login screen. This and rebooting are the only consistent workarounds to this problem I found.

As you see in SOFTWARE/OS VERSIONS below, I have an NVIDIA GeForce RTX 4070 SUPER GPU. I have the latest `nvidia`, `nvidia-utils`, and `lib32-nvidia-utils` packages installed for the drivers. I don't know if this problem is specific to Wayland, NVIDIA, or my Odyssey G65B monitor, or a combination of them, so I am not sure how easily other people could reproduce this problem, but I can reproduce it consistently using the following steps.

STEPS TO REPRODUCE
1. Make sure to use a Wayland session and a 240Hz refresh rate monitor.
2. Let the screen turn off due to inactivity and let it go to standby mode.
3. Try to wake the system by moving the mouse or pressing the keyboard.

OBSERVED RESULT
KDE plays some system sounds, which seem to indicate that the system wakes up, and the monitor does act like it picks up a signal, but it doesn't get a signal and goes back to standby mode. The system is awake, however, and you can log in and operate it blindly.

EXPECTED RESULT
The screen wakes up and shows the login screen, so I can log in and continue the session.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.13.0
Qt Version: 6.9.0
Kernel Version: 6.14.3-arch1-1 (64-bit)
Graphics Platform: Wayland
Processors: 28 × Intel® Core™ i7-14700K
Memory: 31.1 GiB of RAM
Graphics Processor: NVIDIA GeForce RTX 4070 SUPER
Manufacturer: ASUS

ADDITIONAL INFORMATION
I first reported this issue in the Arch forum to try and find a solution: https://bbs.archlinux.org/viewtopic.php?pid=2238190#p2238190. There, I discovered most of the details that I report now (like the problem being specific to Wayland and 240Hz refresh rate), but I didn't find a solution, and the conclusion was that I should report this problem here.