Craft storage. Can store a good amount of yarn and household tools in there from the looks of it. Add some cute lights and a little rug.
If you have cats, you could make it their "bathroom" depending on the location. Put up a curtain, put their box, maybe even the littler and what not, back there, close the curtain. Just make sure the curtain is nice.
Ergonomic editing/workstation with screens wrapping on that sloped part and reclining chair under it, colour calibrated etc. Sound-wise this would suck and it would mean sacrificing having monitors for headphones but could work as a secondary home station if you have a larger space where you can bring collaborators etc at the studio for example and you use this at home.
If it's directly adjacent the door then add some shelves and racks for shoes and jackets. Or a chair where you can wait for Uma Thurman to walk by while you hold a shotgun full of rocksalt.
Gaming area, or if you have a security system and smart home stuff I’d probably make it into a smart home centre with screens and controls for all the devices and security stuff