This is the first time. On plasma 5.24, the alt gr only seems to work partially. I can use it to type all the third levels except for ~,´ and `signs. I can type them in a browser or any gtk app just fine, just not in kde applications itself (konsole, kate, dolphin whatever....). Any ideas?

I figured it out. I enabled the accented/alternative character input feature. Once I deleted the line in /etc/environment, I got the key combos back. Pitty. That feature's great but apparently it's still very buggy. The bug was first reported in 2020. If QT_IM_MODULE is set to whatever, the accent and dead keys don't work. Not solved yet.