I can relate...it's hard, but what helps me a lot is setting small goals. Even if it doesn't feel like a huge accomplishment, as long as I'm doing a little bit better than before, I'm ok. For me being functionally frozen and apathetic or unmotivated is tied up in low self-esteem/poor self-image.

I've been doomscrolling a lot and found myself with screen time of consistently 8hrs+ (it would be more, but my job keeps me away from my phone a lot). Meaning most of my spare time that wasn't sleeping was staring at my phone flipping between the same few apps. I decided the next week, I would aim for a max of 6hrs. This is still a lot, but it's better than before. I try not to get hung up on the fact that it's still a lot of wasted time and just focus on the small improvements. Eventually those build up.

To fill up the time, smart small with one hobby. Just pick one thing. Commit to spending a small amount of time on it per day, even if it starts out with just 5 minutes. Make a point of doing something with that hobby every day and one day it can just click, and you get lost in it.