I saw this post and meant to respond to it.
I can actually relate to this a lot. I moved back to the UK from the US about 10 years ago and having not been to university here, but in the US, I didn't have that friendship group like most people. I made most of my friends through dance classes and for a while I had a nice little gang. But one by one they dropped off - moved to the suburbs and got married, moved to another country/their home country, just dropped off the radar altogether until only a small handful was left. Then I joined a dance company with extremely long rehearsal hours and that became my life (and my friendship group). I was so happy and having tons of fun. But after two years, the physical demand got too much and I left. And I never heard from one of those 'friends' again. Not a single one. When I left the company, I was disowned. Over the next few years, I struggled to maintain friendships, probably a perfect storm of ADHD, life stage, nature of living in a big city.
I have always found it a lot more difficult here than in the US. I'm still friends with my college friends. I have another group of American friends who I do a zoom call with every week and we do a yearly meet up. On my down days where I realise that I have close to 0 friends in London, I remember that I have a couple of great groups in the U.S.
I suppose it's a roundabout way of saying that I hope you don't feel it reflects on you as a person. Life circumstances sometimes just see us ending up with a small - or non existent - group. It's nothing that can't be worked on. I don't know how old you are and you don't have to say, but have you tried Bumble? They have a 'friend' version, it's not just for dating. There so many options to socialise, but it's like dating in a way - you have to put yourself out there and stay consistent, and not get discouraged when one or two fall through, just keep going until something sticks!