Your feed URL is you profile URL + ".rss" on the end...

For example I have:
https://qoto.org/@freeschool.rss

Your feed URL is [instance]/users/[username].rss or .atom,

Mastodon has built-in #RSS and #Atom feeds you can load in a feeder or browser!

Any good RSS browser out there to go load 100 posts instead of typical 20 last posts?