I generally try: /rss, /feed, /index.xml, /rss.xml, /feed.xml, etc. And at various root or /directory/* locations. https://blog.jim-nielsen.com/2021/feed-urls/ is a good article with statistics on naming.

I've been adding to my feeds.opml since reddit started dying in ~2015 and now I'm up to around ~1700 feeds and mostly independent from aggregators; though I still collect new feeds from HN/IRC/etc. Mostly I just always make a point to look for them whenever I read something cool on the web.