For self education? Things that are fun to make incremental progress with.

What worked for me was writing an image editor. Lots of different filters and effects I could add to it.

Then games; if you do that, start with minesweeper or chess (without AI), add features and complexity to do whatever seems fun. You don't need to bother with a fancy game engine at this level, vanilla JavaScript or python or whatever else you're using is good enough, everything is good enough.

If you love sounds and how they work, make a sound processor. Music, procedural music composition.

Main thing is just keep yourself excited for the next step; what that means for you is something only you can answer.