Some gyms have automated belay equipment. It’s a bit clunky and not everyone likes using them but they do exist and do work.
I have always climbed with a partner but we have also included other people into our group who needed a belay partner. I would think that it’s definitely possible to find a partner for the day but it is easier to just bring your own.
There is also bouldering, which doesn’t require a partner but doesn’t go as high either.
It seems like most of the big ideas have been covered, so here’s a small one.
Rock climbing equipment (shoes and harness) and membership to a climbing gym. It’s different, fun, gets you exercise and exposure to more/different people.