The "Happy Journal" probably sounds dumb but I can honestly say that something like it was an enormous part in helping my depression and mental health. Often times when other people tell us stuff we dismiss it because they could be lying, or they don't REALLY know us or whatever our brains tell us to dismiss what they're saying. So having something tangible, creating physical evidence of your progress or even your happy moments is something that your mind will have a hard time arguing against or justifying because it is right there in front of you.
I bought a whiteboard and had a "Goal List" that started out extremely small with things I was going to do anyways. So it had stuff like "Get out of bed" which as anyone with depression knows is a fucking achievement lol. Check it off every day. Shower. Eat lunch. Respond to one text from a friend. Things like that. And it sounds so small and nothing but at the end of the week when you look back, you can see all the things that you actually did. That it wasn't just empty space but moments where you tried. And even if you didn't accomplish some of them the idea is to inundate yourself with a lot of small things so that missing one or three or five isn't a big deal at all.
Then you work your way up. Small steps, from things you do anyways, to small things you want or need to do like "throw out that old monitor" or "grind levels in WoW for an hour". It was...really important to me when I was getting better. I suggest for people also struggling who haven't tried this to give it a shot as it's very low effort but may show some actual results, even small ones.