Strange input field behavior

This bug affects multiple QT applications:

For instance the application OpenRGB. I can select values in several input fields at the same time (see screenshot). If I select a value and press any key on the numpad afterwards, the keystroke is not accepted. The selected value will not be deleted. However, if I click into that field again, so the cursor is behind the value (see screenshot value 0) I am able to use the numpad.

In KeePass that is a password management utility. I select for instance a username in the input field of the same name ("Benutzername"): username@example.com. I would expect that any pressed key from my keyboard would delete the username and just the letter from the keyboard would appear. However any keyboard input is added to the field above ("Titel").

Highlight username@example.com, press keys a, b, c. You can see the input in field "Titel" with Exampleabc.

I am at a bit of a loss. So I created an installation usb stick, with Manjaro in the latest version. I started the USB stick and installed KeePass in the live session. The input fields worked correctly. In addition, I set up a virtual machine, with a Manjaro installation. So far everything works here, too. I would now implement all possible changes to the VM, that I applied to my system there. Perhaps one comes so on the reason for the described problems. Currently, I do not expect that I will find it. It can not be that I now have to reinstall my system because of something like that?