I’ve noticed that problem occurs with all applications I’ve tested: Notes, TextEdit and Brave Browser.
I’ve also verified that the problem occurs the same way with the following combinations:
viewport + windowed mode
viewport + fullscreen
scaled + windowed mode
scaled + fullscreen
I’ve noticed that the problem goes away if I use the mouse to switch to another application and switch back to the application where I want to select something. Then if I start typing in that application, the mouse cursor disappears and when I start moving the mouse again, the mouse cursor appears again and the odd selection behavior comes back again.
I’m having the same issue. From time to time a client is unable to connect and the server displays the message that the desktop is not available. For example, I’ve observed that a client can connect and work for a few hours, then the user closes the session and an hour later tries to connect again, but no longer can, because the desktop is not being shared. Rebooting the server or shutting it down and starting it up again doesn’t help, rebooting the computer sometimes helps, but not every time.