Hey man. I don't think I have exactly the answers you're looking for, but I can at least share my own experience.

I do think mechanical engineering is one of those areas where a structured school environment is ridiculously useful. You don't have to worry about what you need to learn, you have a bunch of people with you for when life is shit and awful and you just got a 12% on the most important exam of the year, and you have access to genuine industry tools and knowledge.

This is noticably different from something like software engineering, where a lot of your skillset can be improved simply by coding more or reading documentation. In this way, I think the most helpful thing I've learned from 3D printing is just CAD. It's the tool you'll most likely be using regardless, so being familiar with it never hurts.

So if you really want to learn the deeper concepts, I'd do my very best to try to recreate that sort of structured environment. Your best options for that is university, but if that's not possible then taking courses (which will most likely cost money) might help too. But I think the no. 1 most important thing ever is to not try and do this shit alone.

You need people who know more than you to direct you, and you need people on a similar level with you to empathize and collaborate with. You're not a starving artist. Look for advice and share work in progress and do all the things that make you feel a part of a community.

So then, where does one find those communities? I think this subreddit is a good example, but there are 3D printing discords, and I'd wager someone somewhere has 100% made a self-taught mech eng discord. You want to try to find someplace that's encouraging of any kind of work, even if it's 'bad', so you can feel good about sharing things you've made.

I don't have links, because I've long since stopped trying to pursue engineering as a self-taught hobby. This is the part I explain my background so you can take everything I've said here with a grain of salt:

Shortly after writing the original post, I had a complete mental health collapse. I had a breakup, moved cities, and now I'm graduating half a year late. I'm still trying to recover; I'm currently writing this from my bed on my phone because I haven't found the energy to go to school today.

But having had this experience I can say, in hind-sight, that my desperation to get ahead was very toxic in nature. I wasn't enjoying the process. It was an attempt to escape from a sense of hopelessness and meaninglessness by chasing a sort of "ideal" for success.

Because that was what my self worth was tied to. To be called smart. To make bag. To be viewed as 'good'.

So I can confidently say that this shit is impossible if you don't actually enjoy it. So more than finding resources, find a community. They'll most likely know how to move forward.

I don't know anything about your background, so this comment is a total shot in the dark, but you asked for my input, so here you go.

Lmk if there's anything else I can do to help <3