Not sure if I'm just socially unlucky or too insufferable to have true friends

I'm 21M, and since my teens, maintaining friendships has always been one of my struggles, despite the desire to have loads of friends around me. To this day, I don't have a friend group, people I talk to have much closer friends and leave me out all the time. I had somewhat of a group in secondary school but we barely hung out or spoke outside of school. Once we finished GCSE's, we drifted apart. During sixth form, I had managed to make two so-called 'best friends' and we stayed in contact even after school and uni. We used to chat and go out for drinks, food etc., but we went on our first holiday in June which I thought was really fun, but once we got back home, I received a message from our group chat a week later saying they didn't want to hang out with me anymore, claiming that my interests were just too different from them and they had ran out of things to talk to me about, which absolutely tore me apart. I hate looking back on photos where I'm having a good time with people who don't even contact me anymore.
My Uni experience was lacklustre and I never found myself fitting in with friend groups. Whilst I graduated with two friends, they live about 5 hours away from me so meeting up whenever is tricky, especially since we all work now. It's more local town friends I'm majorly struggling to maintain, it seems. The thing is I'm always putting myself out there and putting genuine effort in to connect with others, but I get little to nothing back. If I didn't try, I'd still get nothing, yet trying doesn't work either. I'm CONSTANTLY the one to message first or call first, but I get nothing back, yet these people will want to be friends with others, but when it comes to me, I seem to be a big problem to them. Making acquaintances feels like a piece of cake, but getting to the friendship level is practically impossible.
I'd say I'm extroverted and sociable and I believe I'm capable of having conversations with most people, but I think there's cues I'm just blind to (doesn't help that I have ADHD). I seem to have a knack for picking up introverts who don't put effort into friendships, but also other extroverts don't want to be around me either, so I just repel everyone and anyone, apparently. I've always tried inviting people to go clubs, go on hikes, cinema, and many other social activities, but they constantly reject my invites yet will go out and do said things without me...it stings so much. I dislike doing things solo (apart from gym) because it just makes me feel even lonelier and its upsetting having nobody to talk to or find solace in. People have said that i'm funny, witty, creative, friendly, then why am I basically alone still? I'm authentically myself, but I do think there are subtle things I need to work on. I dislike my weight atm which is why I workout a lot so I can become muscular and more desirable; I know this sounds shallow and might not ultimately improve my social outlook, but I believe it will bring me more confidence in myself.
I just want some honest advice on what to do, because as much as I just want to give up, I can't because that won't improve anything. I keep staying optimistic on the outside, but I'm suffering a lot internally.