My husband and I both have friends.
I have school friends, they live around the country, a couple are the other side of the city and we only meet up in person every couple of months but we're in weekly contact on messenger.
Uni friends who live all around the country and internationally who I see once a year and whatsapp once a month ish.
My sister who lives very locally who I see weekly and message regularly. My parents who live locally and I see weekly for a meal and sometimes shows and quizzes.
The school mums, only a few of them now our kids are in high school, but we meet up every month or so for drinks or food and we've got a festival and gigs planned together.
The partners of my husbands' mates, some I know from school but most I've got to know as adults. We chat in a whastapp without the boys, we go out for brunch, nights out, family BBQs, holidays, weekends away, local walks, park meet ups etc.
Rugby friends - all our kids play the sport, my husband plays, we go to our local club on Saturdays and Sundays to watch everyone play their games, to watch club and international games, for social events like parties, fundraisers, etc, and just for sitting around chatting in an intergenerational welcoming space where we all belong and have our own mates.
We all have other hobbies and interests and jobs and all the more casual friends and connections through that. Neighbours, people we volunteer with in the community.
Not all sports are as social but I don't think you'll find what you're looking for at a leisure centre. Maybe something with more of a club or membership model like tennis or golf. At our community centre where I'm involved, we have groups which people who are lonely or just want to meet new people can come to, some are daytime, some evening. Some are about learning a skill like embroidering or cooking but involve making friends and others are more social focused. We have a mix of ages at them and they're well attended. Could be worth looking into voluntary groups in your area?