1. How do I fix this? Is this burnout or depression?
This is adulthood and you need to get a life beyond your job. Find hobbies, meet people etc. Learn to cook and do things yourself. I would never befriend somebody that just order foods, works and waste their time in social media.
Also visit a therapist. You need it very badly. Do it before you waste all your life not even knowing what you want.
2. How do I get ambition back and get rid of the envy?
Why do you need even more ambition?
3. How do I retrain the delayed gratification & work on hard things muscle? I think I'll start going to the gym and lift weights.
Don't buy this Jordan Peterson or Youtube motivation crap. You are thinking of that solution because you spend a lot of time in social media.
It is all a lie. Yes, you should exercise regularly, but there are at least thousands of sports. Why do the one that is the most efficient on improving your looks, rather than having some good mobility and agility? Or learn to swim properly? And the list goes on.
That's just you trying to be more and more competitive. You'll just waste your whole life on self-improvement. Find something that isn't about winning or growing bigger.
Look for a psychologist, you look very lost.