This is a laptop and I am using KDE Plasma and the standard kernel.
In the last 10 or so days it happened two or three times that the mouse cursor disappeared.
No idea why? Kernel, Plasma???
I rebooted but I would be happy if there is a possibility to restart something to get it back.
Replug mouse?
Sorry, should have said that this is mouse via touchpad.
Are you using any themes other than breeze?
I am just using Breeze theme.
You don’t happen to use the zoom effect on the desktop at all do you? The only thing I can really find thats close to recent is from febuary and it was cause by the zoom effect.
Sorry I can’t be of more help but I have to head off to bed, hopefully you can get this sorted.
Yes, I actually didn’t use any zoom effect for a long time.
Sleep well! 
When you say “disappeared”, do you mean it became invisible and you were still able to click on things, or was it completely dead?
The mouse cursor disappeared and when I clicked I didn’t see anything happening on the screen.
But to be honest, without a mouse cursor I don’t know where the click will happen, if it happened at all.
Without a mouse cursor I switched to the open apps and closed them. Then I switched to an open terminal and issued sudo reboot
An easy way to test this try a right click to bring up a context menu.
Something else I forgot to ask the other night is are you using X11 or Wayland?
I think I did try right-click but nothing happened. This is X11.
logs logs where are the logs?
https://discovery.endeavouros.com/forum-log-tool-options/how-to-include-systemlogs-in-your-post/2021/03/
I grepped the logs for mouse and there was nothing to be found in terms of errors.
Next time it happens I will post logs. Which pattern should I grep? Or do you want to see the full logs?
Boot log could tell something that causes it also without there is an error with the mouse itself. And hardware info would make it possible to research in any way.
Ok will do next time when it happens.