I'm unfamiliar with SDL but it sounds like a start. But it makes sense for such a feature to not already be in as it would seem like a sketchy feature to have in the API.
I was personally interested in making a character animate as a part of a stream, like a vtuber type of thing but I had particular features I wanted to make myself that other vtuber software doesn't have like making the character appear to draw on a tablet when my cursor is on the screen tablet.
I would also imagine somebody making a map in a game that windowed and clicking and dragging to move about but having the mouse leave the window would interrupt that motion. Little things like that that make interfaces a bit more comfortable.