KWin had the shortcut built in and enabled by default at some point, but I removed it, for Plasma 6 IIRC. If shortcuts still work, you can switch to a different tty and execute kwin_wayland --replace for a similar effect - which you can’t hit accidentally and which might not crash all the apps with it.

fully up to date Debian Stable

Now that’s quite the oxymoron… Debian stable is on Plasma 5.27.5, that’s 6 bugfix-only releases behind the upstream 5.27 branch, which itself is very old by now and has seen its last release almost a year ago.

That all is to say, if you want to avoid crashes, avoid Debian stable.

I don’t know, but I hope so. With my Nvidia card, I don’t know how many times my display got hung up and had to ctrl-alt-# into a text shell to restart the login manager to get it to work again.