Making friends after university

I didn't make a single friend at university due to covid and lack of initiative. I never kept in touch with school friends because I thought university would be different.

I have a job now and my colleagues are mostly a lot older than me (i.e., have kids...).
I'm also now at an age where it's odd not to have had any of the typical
young adult social experiences.

Any tips TSR?
Where do early 20s adults meet? (I don't live near a city btw)

Join a club, sports or other or become a benevolent worker. Look on the internet and see what’s going on in your area. Alternatively contact a few people from your old school. Say that you are back in the area and wondered if they’d like to meet up. Although, as it seems that you dropped them without looking back, thinking that you would find others at Uni, I can’t guarantee that they will be receptive, but it is worth a try. Friendships need to be maintained. It’s not complicated with all the social media available today to like a story, or write a quick text once every few months.
You say that you don’t live in a town, but don’t say if you’re male or female, but even the smallest of country villages normally have some sort of sports teams even if it’s just the local pubs darts team. There are things like young farmers, which you can join even if you don’t farm as much of what they do is just to keep social contact between young adults in rural areas.
If we knew what your interests are it would be easier to help, but it’s never too late to start making friends if you’re willing to step out of your comfort zone