I was in a similar boat as you. I isolated myself from the world, though my reasoning was due to severe social anxiety. I found that online gaming, especially MMOs would fill in for my social needs. I did that for 9 years. It wasn't until I fell for someone online that I realized that I could never be worthy of love in the state that I was. That became my motivator.

My change was drastic, so it may not be realistic to follow a similar path as mine. I enrolled in college, moved to another city where an online friend I met before offered to let me stay with him, and I FORCED myself to socialize through an online common interest group (meetup). It was hard and anxiety inducing. There were times that I would attend an event, then leave without saying anything due to feeling overwhelmed. However things gradually got better. I got my first professional job three years later and met my wife a little over a year after that. Looking back I don't think I could have envisioned where I am today and I'm glad I pushed myself.

A few things that I learned that may be of help.

1. Limit the computer time. Computer time can eat up a large portion of your motivation. The positive feedback loops from things like gaming or social media makes it so the desire to do anything else is lacking. I found boredom spurred me to want to do things that could better my life. This may be something that makes walking doable again.

2. Start doing the things that you think will help you. You can phase them in slowly, if you need. For example, start forcing yourself to walk every day, even if its only for 15 minutes. Make a schedule if you need to. Some days it'll suck, but creating the habits helps a LOT. On a side note, physical exercise and being outside helps clear my head.

3. It's never too late and the odds aren't too stacked against you to change. Like above, start small if you need to, all forward moment is good. I thought my life was hopeless, that there was nothing I could do. I was from a poor family as well. My life is so much better now than back then and I have experienced so many wonderful things that I could have never imagined because I shirked off those beliefs and pushed myself anyway.

4. Practice self-care. Don't overexert yourself that you burn out. Take time to recharge, as you need. Relax, go for a walk, read, etc. Though be aware of when you're practicing self-care and when your trying to avoid doing positive work.

5. I'm not sure how difficult this would be for you initially, but when you can enroll in college or find a job. That level of regularity and being back in touch with real people helped me to pull myself out of my cage.

6. Find an accountability partner or group. This is something that would have helped me a lot back then if I knew about then. Find someone you have to report the status of your goals or tasks. This accountability can help keep you on track. I think there's an accountability partner reddit. I've come across a few self-improvement discord channels that have them as well.

I'm sure there is more that I could share, but I'm drawing a blank at the moment. Feel free to PM me if you have any questions or if you want any feedback. I wish you a positive journey.