My serial monitor window opens frozen, without any output or possibility to input, or even activate the window. Sketch is very simple, but behavior is same even with empty sketch, so I assume problem is not in sketch. I also checked if sketch is uploaded correctly by uploading simple sketch with blinking diode, which worked.
Same behavior with Arduino Nano and Uno.
I tried to reinstall IDE, uninstalled, removed and reinstalled serial driver (ch340) with no success.
I can see Serial monitor window only on windows taskbar, it won't activate after click.
Until now I haven't had any significant problems with IDE or serial monitor for years.