Generating SD video

I am looking for a replacement for flaky Android TV boxes, to drive an analogue TV/monitor. The Android TV boxes often have a composite video output, and that should be possible to get using an old graphics card with video out, or an external converter.

But I should get much higher quality using RGB video instead of composite, and running the display at the correct resolution. In the good/bad old days you could add a modeline for SD video to the X11 config file, to make it work (on some, but not all, cards).

How do you do that in the modern Xorg/Wayland world?

The interesting resolutions should be 720x576, 768x576 and 1024x576 (for 16:9). All at 50Hz interlaced.