Ultimately the best way to meet people, and especially to grow and maintain those connections, is to have the same hobbies as them.
Do you like sports? Join an adult league.
Do you like reading? Join a book club. Do you like tabletop games? Use Reddit’s r/LFG, or look for a local meetup group, and find some people there.
Ultimately it’s hard to make new friends when you have nothing to tie you to them long term.
People have set routines, and it can be difficult to have them make time for a stranger initially.
But if you join group doing something you enjoy, you already a part of their lives through that. You also have an easy source of conversation, talking about whatever your joint interest is.