The in-depth discussions part (i.e. things like seminars) is probably difficult without registering for a class in some manner—which, in turn, is difficult at a traditional university without enrolling, outside of some continuing ed program. My undergrad university library is also accessible (at least if you look like you belong) post-COVID in the sense that you don't have to card in but even I (as an alum and moderately large donor) would almost certainly have to pay an annual access fee to check something out. It also has some generally accessible activities in January but you need to know where to look.

Universities/colleges are a pretty good source of cultural activities and other things in a town but their classes, and to a lesser degree libraries (it depends as some libraries let people just walk-in though not check-out material; others control access pretty tightly), are not really public resources.