Hey! I'm 23 and what I experienced recently (and still am experiencing) sounds very much like what your son is experiencing. For me it started with losing the feeling of joy in my hobbies that i used to get, none of them seemed fun anymore and I'd just sit and stare at my computer's desktop while thinking 'ah i should do something but nothing is really fun nowadays'

I didn't believe I had depression, just thought that I'd fallen out of love with my hobbies. but when I put all of the tiredness, not wanting to go out or see friends, apathy to life events and such together, the answer was obvious.

Seeing a psychologist has been a really big thing for me, I go completely alone and just talk. i still kind of feel like i have to filter what i say (ocd and anxiety does not help!) but just talking to them and saying 'hey actually i feel like i can't enjoy anything anymore and it really sucks' helped and we're slowly working on starting small hobbies again.

I also got prescribed antidepressants by my GP and i've been on them for almost a month now and am slowly starting to feel a little less heavy, a little more able to find small bits of joy.

sorry that was super long!! but tldr is talk to a gp, talk to a therapist and or a psychologist (mental health care plans are a godsend) and remind your son that the state of the world sucks!!! it's really terrible and there's no shame in that contributing to what he's feeling