Hi! I’m in a similar place - trying to find interesting active newsgroups that aren’t completely overrun with spam. Here are a few that seem to still be going strong:

alt.fan.usenet alt.folklore.computers rec.arts.sf.written rec.arts.tv rec.food.cooking alt.home.repair alt.woodworking

One thing I stumbled upon that was super helpful was my news provider’s daily Innreport, which includes a listing of request counts by newsgroup (example here: http://www.eternal-september.org/stats/news-notice.2023.06.21-04.00.02.html#nnrpd_group). Going through those lists helped me find other active groups for more niche interests than the ones listed above.

Good luck!