SUMMARY Under the keyboard settings and Advanced tab it is possible to set a key for changing to the third level. This is not working for the right alt key, but for the left alt key or the context menu key. STEPS TO REPRODUCE 1. Use an QWRTY keyboard and set the keyboard layout to german (i used the at one to be specific) 2. open the advance tab and select "Right Alt" under "Key to choose 3rd level" 3. click apply 4. open a textfile and press right-alt+q OBSERVED RESULT the character "q" is printed. EXPECTED RESULT the character "@" should be printed. it works if you chose left alt under the settings and press left-alt+q. SOFTWARE/OS VERSIONS Linux/KDE Plasma: KDE neon 5.22 User Edition (available in About System) KDE Plasma Version: 5.22.4 KDE Frameworks Version: 5.84.0 Qt Version: 5.15.3 Kernel Version: 5.8.0-63-generic (64-bit) Graphics Platform: X11 ADDITIONAL INFORMATION KDE rules.
Could you try on other DE - Gnome etc.? If the behavior is the same, I think it's upstream problem. In this case, please report there and provide an issue link: https://gitlab.freedesktop.org/xkeyboard-config/xkeyboard-config
This is not a but. Apparently my right alt key broke as i started messing around with the keyboard layout. Sorry for wasting your time!