(Apologies in advance: I am neither a kernel expert nor a graphics expert, so the following explanation is my understanding based on what I've learned so far; it may be lacking details or containing factual inaccuracies.)
So SDL has things called "render drivers," which are what causes the thing you want to display to go through the transformations needed to display it on screen (like OpenGL), and other things called "video drivers," which are what takes the thus-transformed data and puts it on a screen. This Reddit post has a bit more. I use the `fbcon` or `kmsdrm` video drivers and the `software` rendering driver. This works great for the uses to which I've put it so far (90s DOS games), because even tiny modern computers (like a RasPi5) have so many orders of magnitude more of speed, memory bandwidth, etc. that it Just Doesn't Matter :tm: how inefficient those bits of the pipeline are.
I presume that if I tried to convince a modern 3D game to run like this, it would either
a. Catch fire;
b. Refuse;
c. Call my mother and tell her I'm a bad person; or
d. All of the above, simultaneously.
But hey, it works great for what I'm doing at the moment!