writing; long or short stories (Stephen King’s On Writing if you wanted a starting point), maybe set up an account on Medium (for example) and start posting? Maybe link it to your own patreon page when you feel comfortable?
drawing; from short form comics to graphic novels (lots of youtube channels but a jump off point for structured lessons could be drawabox.com)
music (again multiple youtube series and music tab sites, may however cost more buying an instrument and even more if you wanted to set up some sort of production suite - computer/software/audio equipment)
video; wouldn’t know where to start here for actually learning the skillset but the outlay for equipment could be potentially expensive though a smartphone with a camera could be sufficient to begin with (if you want inspiration look up a youtube series on video essays called Every Frame a Painting). If you develop drawing as a skillset you may want to veer into animation instead.
How do I build an art form that sounds fun, but I have no idea how to do that, it seems a lot of art forms have already been discovered
Completely up to you: