Great advice on this thread (Mumsnet is part of our tribe) and just echoing the two last posts here.
Firstly, I think it's quite important to have realistic expectations.
If you've had early trauma experiences you tend to look for "family replacements" to heal that wound.
Realistically most friendships are light and situational. People are mainly concerned with their kids and partner. We can have a great time with people without it being "ride or die". Or even seeing that person again.
I'm a nice person on an ad hoc basis, but I wouldn't want an intense friendship with someone as an adult where I felt I was expected to be a replacement mum or sister figure.
For things like loneliness, anxiety, I've found it best to develop my own solitary self care practices.
Meditation helps with emotional regulation and acceptance (Quakers and Buddhists have the social aspect and won't evangelise you, if you have time and money do the Krishnamurti centre).
I found psychedelics in Amsterdam very helpful for trauma/negative thinking. Never personally got on with therapy. I like Reddit and Mumsnet for chat and advice.
Solitary physical exercise like running or yoga. Journalling on Day One was good but I haven't found the need recently. Self care is an ongoing flexible thing not a quick fix ...so give it 1-2 years, try different things.
I agree that if you are interested in turbo charging your social life it is a numbers game.
Go to one new social thing every month or so....look up Meetups, find hobby/sports groups, have a weekend in a big city and attend groups there.
Go to "Shut up and write" events even if you only have paperwork to complete. Treat it like a part time job.
You're not there on a specific mission to make friends, you're there to get out of the house and practice your social skills every month. Its a win if you turn up.
You'll meet lots of weirdos and have some hellish evenings. But after a year or two you'll have identified the "nice" social spaces, you'll be a regular.
I wouldn't chase 1-1 friendships immediately, just turn up and keep it light.
I find the most welcoming spaces have a mix of genders, ages, backgrounds, and regulars and newbies. They tend to attract similar nice people so once you've found them you're in.
I echo pps who say small all female groups can be hard to crack...when I was just socialising trying to get a close all female "girl gang" I found it horrific!
Keeping a more open, pragmatic, and realistic mind about how to get my social needs met was very helpful.