Putting it up front that I'm neurotypical so if this advice/lived experience isn't helpful to you I apologize. Just trying to help out a fellow comrade deal with neurotypicals.

Familiarity is a major component of it- just being present consistently at a place around the same group of people in an area of shared interest. There will be functions you attend that will have groups actively looking to include new people and ones who really aren't. You may just unfortunately be running into more of the second type of group in recent hobby group experiences.

Asking groups if they mind if you join in even if they seem somewhat closed-off initially may be a route in- a lot of neurotypicals in established or semi-established group setting may not consciously be thinking to add people into their activities but would welcome at least letting someone participate if approached.

Generally in settings with pre-established groups where you're the outsider really taking an active-listening role and just feeling out the relationship between members of the group is a good way to begin to learn the dynamics. Also you don't necessarily need to be (and likely don't want to be initially) an extremely active speaking member in this scenario since the interplay between existing members is a part of the existing group dynamic that no one will have a great feel for when meeting people who already know each other early on. Perhaps at first just try enjoying being a part of the activity with the group and not taking an especially social (speaking) role if you haven't participated as a member in the group context many times before.

Also be looking for individual(s) who seem more open to trying to get your input/participation when you find yourself in group dynamics. At least in my life I try to provide a sort of on-ramp to conversation/group inclusion when new people are trying to test out the waters of pre-established group dynamics. It doesn't necessarily mean that I am trying to become a close friend to anyone in particular, but I (and a hopeful person filling this role you can hopefully identify) am the person trying to help both you feel out if this group is a good fit for you and the group to see if it feels you're a good fit for it. In my experience I do this in a few ways: explicitly asking the new person for their thoughts/participation in said thing, ensuring that in-jokes/referenced stories are explained/retold so that the new person feels included in the meta-conversation, and usually at the end kinda just singling new people out and thanking them for joining us I'm whatever we were all doing if I feel I personally or the group enjoyed having them participate. Don't assume not getting this acknowledgement at the end means they didn't like you- it might just not be something they do in the way that I do.

I also want to say that I'm sorry things seem to not be going the way you've hoped they would lately with putting yourself out there. That sucks and is a rough feeling for me. Hopefully maybe something I've said may assist with assessing group dynamics and I wish it were as easy as everyone being explicitly up-front with each other to identify mutual interests and companionship.

If you're willing to share some of the hobby groups that may be helpful too.

I also want to say that I am coming at this in as good of faith as I possibly can as a neurotypical, and if I've said something offensive please let me know so I can correct that behavior in the future as the last thing I'd want is to hurt a comrade reaching out.

I'm also willing to answer kind of any question you or others may have if you think my further input may be useful.

in hobby group asking for help with some stumbling block is nice, people like teaching about their own hobby and if you make progress and then thank them you make some small human connection with person. (!nb if you do know how to do it, it might come off manipulative, so don't do this just for talk, but rather ask for real help with real problem)

I'm coming from all and I'm not at all neurodiverse. I'm an extrovert and i usually fit well with groups. I read your posts and maybe i can help. It's hard to assess why by a few posts but i feel you're quite negative, which is understandable because of what you're going through. I wasn't going to post because i didn't think you would relate to what i was saying but another neurotypical posted as well so i figured, why not.

I commend you for putting yourself out there, you seem to be doing great! Don't be so hard on yourself, your inner life reflects on your outer posture. Being so negative you might be choosing topics that are bringing people down, or your body language is putting people off or you aren't being a good conversationalist. Remember, people like to discuss common interests and having fun.

You also seem intelligent, which is something you gotta tone down somewhat in social settings, in general. People just don't care about how smart you are, they won't be impressed and sometimes they might feel bad about themselves. Try to ping pong the discussion with questions about the topic or about the person you're talking to. If the conversation dies, try to think of a related topic that they'd be interested in or ping off something they said. Let people talk to you and show interest. Lead the interaction with your heart, not with your head. That means trying to develop the ability to feel your conversation partner and/or group and letting that feeling do the talking.

Try to learn how to keep a solid eye contact (but don't stare people down, it's all about timing it and breaking it depending on how comfortable the person is) and be mindful of your posture and the way you dress. Now i know this is hell to some people, but if you can't look into people's eyes, try looking at their eyelids, or their nose bridge.

Give people time to get to know you. Sometimes you just gotta be on the sidelines putting your best self out there so people get familiar with you. Try to be relaxed and later on confident. If you're nervous you will make the other person nervous and they won't quite figure out why they're nervous and will leave. Avoid getting too personal too fast. Telling too much about yourself off the bat scares people off. Like grabbing a book and telling a person the highlights of the story then giving them to read it. You're spoiling the adventure of getting to know you.

When you address a group, remember to turn around to face different people as you speak, and not just facing the person who spoke with you last. That way you're including everyone in the conversation. Don't be afraid to share the floor and bring attention to other people who also wanna talk.

I understand I'm telling you something that is difficult because you're neurodiverse, but i truly believe you can do it with practice and dedication and acceptance that you will fail many times in the process until you succeed, much like learning math or the piano. In particular because this goes against what you'd naturally find intuitive. But remember that this is an achievable goal nonetheless.