I find researching random things and scrapbooking/taking notes about it can feel fulfilling. Like every now and again a random thing will interest me so I'll learn about it to keep myself occupied.
Even if you move on before you actually learn anything important about it it's nice to have just made a little collage or written something down instead of just doomscrolling or soemthing.
If you don't like physical note taking your could get notion and make those aesthetic things with cute pictures and stuff, but it's only enjoyable on a computer imo
Also random niche hobbies can be fun. I used to be really into book binding where I handmade and sewed together my own sketchbooks.
Another thing I learnt was crocheting but i never got good enough to finish anything, I still enjoyed it anyway it's just something to do with your hands once you get the hang of it. It's fun to do while watching tv too, so you feel like you accomplished something rather than sitting doing nothing.
Burning music onto cds is also fun. You don't even have to do the cd part tbh you could just make a themed playlist, or you could put them on a usb, but I liked making the album covers that slip into the CD case
Someone replied with decorating which is a good one, like making your own posters or you could just plan how you want your future house/room/garden to look. I used to draw out garden layouts for when I own my own house lol,
I feel like these only would be useful if you're an arty person though
This one's kinda embarassing but I like to just get dressed up and do my makeup even when I'm not going anywhere, idk I call it dress up, it makes you feel good about yourself especially if you've just been inside on your phone doing nothing for days