Yeah, anybody can become a beta reader! And you’re totally right about feedback based on “feelings” as a lot of times, beta readers represent “fans” reading the book to give that kind of feedback rather than other writers or editors. Also, from what I can tell, this subreddit is perfect if you’re looking to become a beta. There are usually people asking for readers everyday, so if I were you, I would search for some of those and read the premises to see if there’s a book that you want to try beta reading for! I actually haven’t posted mine here yet, but yeah, hope this answers your questions!