12 hours later: I'm out of even nonsense ideas. PC is ewaste, be a year or two before I can afford a cheap one from Walmart or smth. I sometimes amaze myself, followed a straightforward installer so wrong it killed my PC. That's actual talent, really.
Least I still got the phone.
Installed Nobura so wrong it killed my windows install, isn't installed, and I can't install any os to any drive
If I get my computer back up I am learning the lesson I am too incompetent for linux
This is a total replacement of original title and body text
wanna share the guide? Also, is there a reason you're using xrandr and not the Plasma system settings app?
https://askubuntu.com/questions/330293/how-do-i-set-a-monitor-resolution-that-is-not-available-in-the-display-settings
Most "user error" caveat possible here, I stopped after step 5 and before step 6 cause it seemed to just put me back into 1080p at 120hz when I tried to go from 2160 30hz to 60hz.
Also I tried using the display config but the native res at 60hz isn't available (max 30) and no 1440p is available double checks that display config in system setting sis the same as the shortcut in right click desktop Yeah I tried the right thing, just doesn't have the option. Windows 10 and 11 do.
Edit: Live disk of Nobura has the res setting I want, just installing that