Hi, i'm writing this post to let everyone know about the issue with the latest arduino release. It seems that serial monitor is currently broken/ not working. This is a huge problem at the moment, because if you use it, you will run into many issues.
it seems that serial monitor isnt switching off after each flash, you have to manually close it yourself
Solution: When compiling, you can disable serial monitor (Not Sure what the issue is, however serial monitor is completly broken/unusable)
I am still not clear what you are having a problem with. Using IDE 2.3.4 with the Serial monitor open I can upload code to a Nano classic, an ESP32 or a Uno R4 WiFi
There is a known issue (and not limited to the latest release (2.3.4) but to IDE 2.x in general (if not mistaken); I think it's limited to Windows. It's said that it relates to boards that use the FTDI chip but your experience might be different.
Which board are you using? What is the serial-to-usb IC on your board?