15 Khz resolution regression on Linux (Ubuntu, Mint)?

I was recently using my old AMD laptop for connecting to a CRT by just using custom xrandr created resolutions, but I discovered that some resolutions don’t work there anymore. For the most part I just get a black screen, no sync rolling or something like that. This affects common interlace (640x480 and 768x576) but also some lower 240p resolutions (e.g. 648x240). With 960x544 I get a picture, but it’s unplayable flickering, 960x272 works fine. The laptop uses an updated Linux Mint 20.1. I was wondering if anyone was experiencing something similar on Linux recently?

I don’t have a way to test SwirchRes right now, but the last few times I used it, it was no longer necessary to create a custom resolution file because it automatically recognizes the resolution of each game.

Switchres was not factor in what I wrote above, because I only created my resolutions manually before. It just happens that I also recently tested switchres on the laptop to see if it makes a difference. It wouldn’t work at all. I tested it on my old desktop, and it worked. Still needs a file (switchres.ini) to be usable because of geometry adjustments though.

I also did a did a test by booting an older version of Mint and also a Debian-derived distro, and both did not provide interlace on the laptop either. Very puzzling.

Switchres is a new implementation, the previous one is no longer used, I’m not sure but I think they abandoned it from 1.9.2. What I understand is that a file with resolutions is already needed, it makes it automatic for whatever, console or arcade.

Check that you have installed these two dependencies: libx11-dev libxrandr-dev