Some ideas are:
Make the most of the fact there are a few of you in your immediate family- 5 is a great number for a BBQ, so carry on having fun days out and BBQs and holidays in your immediate family, as family can be very companionable.
Think about therapy. It sounds like you could do with someone to listen to you, vent to, and to reflect on things with and I find a therapist the best for this, it also means that they listen in a different way than a friend. You could talk about this issue in therapy, but more than anything, gain a listening ear for you, you really do deserve this.
Meet Up is a great way to meet people who are similar in wanting to find friends or enjoy the hobby or whatever brings you together. The problem with lots of things like an exercise class is that many people will go, but not really be on the look out for new friends, same with the school gates. It's pretty obvious if people go to Meet Ups they want to meet other people!
Think about using a friendship app, such as Bumble which is not just for dating.
Go to hobbies which you enjoy, but don't bother to ask anyone for coffee, just focus on enjoying the hobby and the socializing that comes from joining in, choirs are great for this as people chat, meet up for the event, so there's fun in being part of a group without it necessarily leading to a full on friendship.
Just a few ideas, perhaps that wasn't what you were looking for, as it's still focusing on friends but I saw a really good post recently about expanding out what you think of as 'friendship', and that you might have quite a few acquaintances, a few people in a hobby circle, and perhaps one or two people who you can chat with at a deeper level, it helped me think about socializing in a wider way- I would also add in being a friendly neighbour (only saying hi, odd bit of chat, not going round with home-made cookies) and being chatty in parks, shops, dog walking if people seem willing to chat or just smile, all this helps you feel more connected.