This has been driving me crazy for a while, but I never did anything about it: Whenever I use the keyboard to delete a file in the file manager using the DEL key, or go back a directory using BACKSPACE, or some everyday task like that, the computer beeps really loud, and almost makes me jump out of my chair. Disabling the speaker in ALSA Mixer does not work, and setting the volume to zero also does not help. So here is how to get rid of that beep:
In a terminal, write:
$ xset -b
You can of course also put this in your startup script (.bashrc or something) to make it permanent.
In KDE, you should be also able to disable the PC speaker beep via the System Settings GUI: https://wiki.archlinux.org/title/PC_speaker#KDE_Plasma
(the linked article also describes even more methods of disabling it)