jokes aside tumblr is actually pretty great for making friends within fandoms imo <3
you can just follow the people you like and unless you follow people who engage in drama it's pretty peaceful. your dash is pretty much your little bubble that's closed off from the rest of tumblr, that's why you generally don't see a lot of fandom wars there because everyone only interacts with content they enjoy. one way people love to make friends on tumblr is sending anon messages and revealing themselves when they feel comfortable, or reblogging each others posts and writing something in the tags. i've been on tumblr for years, in different communities, and i've met lots really lovely people