Look into Rachel Bailey. Here's a start:
https://rachel-bailey.com/240/
Also look at her joint problem solving stuff.
I've used her paid programs and they are great, but she has a lot of free stuff out there, too.
I will say that from your description, I'm not entirely sure what you want him to do, so it's not surprising he doesn't do it. Do you want him to be on screens only two hours a day or is it more that you want him to participate with the family/play/exercise?
Either way, you can set a boundary and still be respectful. See the podcast but basically saying, "Today you get screens for 2 hours. What are some ideas you have to fill the time?" and then helping them through it while not expecting him not to be upset but not letting that upset you. Balancing firmness and respect.
I'm guessing you're low on the firmness because you desperately want to respect him because you didn't feel respected as a child.
The other piece is you have some trigger(s) about his behavior(s). Maybe you are worried he will be always be lazy or never graduate or get a job, make good relationships, etc. You need to be able to separate the behavior from the catastrophic story you're telling yourself.
Excuse my rambling and poor explanation, but Rachel's stuff changed everything for us, and it makes senses when you get it.