Up to and including Raspbian Stretch, I could use a hacked SDL library called SDL12-kms-dispmanx by a developer called vanfanel to run SDL 1.2 code from the console without X. (See here: https://github.com/vanfanel/SDL12-kms-dispmanx)
Now, with Buster, this fails because the dispmanx calls seem to return an incorrect screen size. This seems to be a firmware thing, since the same problems happen when I install the newest firmware on a Stretch based system.
Is there any alternative that works on Buster and that doesn't involve either porting the code to SDL 2 (which would indeed be better, but unfortunately I don't have the time for that) or running X?