Hi,
He's lucky to have a caring mum like you. Please don't think (and don;t tell him either) that most people have a career by now. It's not necessarily true. People spend their twenties making mistakes - being with the wrong person or in the wrong job or with no proper job. It's a time of flux.
But for him to figure out what he wants in life, he needs to become involved with the world again.
I'd start by coaxing him to talk and really listening to him.
Drag him out on a walk with you or ask him to help you tidy the garage/dig the garden or any other longish job you've actually dreamed up just so the two of you can be together, with the focus of an activity. Chat generally at first, don't seem to be prying or sorting him out.
Once he's opened up a bit, you could say that you think he deserves a more interesting and fulfilling life than he currently has. (That's a way of saying things need to change without any judgement in it.)
When I was in my twenties and a real mess, a lovely man I knew a bit got me to draw a square on a piece of paper, then divide it into nine and put an aspect of life that is important for happiness into each box e.g. health, family, money, friends, romance, etc. The only rule is, one of the boxes must be about serving the community/charity work. The other eight are whatever matters to him (music, fashion, travel.)
Then you do something every day - however small towards improving each of those areas of your life. It can be a tiny tiny thing, buit you do one each day for each box. So for health, he could just walk the dog to get fresh air, or drink a litre of water. For charity he could take some clutter to the charity shop for you or pick up some shopping for someone nearby who is housebound. Every day, you write down what you did. Every week you review it and get a bit bolder next week.
He'll see from this that the most amazing changes in life can occur from the tiniest actions. DS2 was a real introvert, stuck at home all the time. But I got him to really stick at a hobby he loved until he got good at it. Then he started chatting online with people interested in the same hobby. Then they met up in a public place. Now they go to gigs together, for BBQs - they have a good life, all from online chat about a shared interest.
It's possible he's depressed, but I'd try a bit of a life overhaul first before getting him dependant on ADs as they have so many side effects. It would be worth getting some counselling though. He may have got past the initial breakdown but a short course of online counselling or a CBT moodgym might really help him.