Anything non technically shouldn't be done/visited in a subreddit or sublemmy, dedicated to it, after the initial "solution". What I mean is, that all those subs are used and commented by people who are also suffering from those issues. This might help for an initial coping strategy and general advice on how to move on, but that's about it.

As cruel as it sounds, but depressed people will drag down others. Mentally ill people will give an advice that could make things worse, if it's past the coping strategy. It can help to talk with people who suffer with similar issues but it won't solve your problems much, as they themselves are sick.

If you have an alcoholic problem, you don't visit the local park with the alcoholic guys sitting on a bench. If your depressed you seek optimistic people who help you to become more optimistic and you don't hang around people suffering and writing depressing notes, on their phone, out of the bed they haven't left in days. Relationship advice on a relationship focused sub sounds smart at first, but then you'll notice they are either unhappy themselves or are in a bad relation right now or are single for being a shy/nerd. What advice could they give?

Lemmy isn't different btw, as it's similar people, just not as many. You have the same risk of being lured by bad advice here as well.

Real therapy can't be done by Reddit and needs professional help and even then it's hard.