It really depends on what sorts of communities you frequent, as the methods for establishing contact and thus friendships and the sorts of people you meet change. Generally, I find it easiest on a place like Discord if you have already have a group of friends on there that share your mutual interests and that are in servers that cater to those mutual interests. While it's not a sure-fire way to find new friends, joining their servers by asking for recommendations and invite links to them can introduce you to new people through a simple task of networking (which is actually a good skill to have IRL, so might as well train it in your free time by making new friends as well). Additionally, Reddit, 4chan, and, to a lesser extent, Discord have specific subreddits, forums, and servers dedicated to specific topics that either the communities you're a part of will be interested in and flock to for discussion. It's pretty easy to find like-minded individuals by jumping into such areas of discussions, though be prepared for a mixed bag as open communities tend to attract all members of a society/community and not all of them are exactly good people.
For a site like this, it's definitely getting into general discussion threads/the live chat and just doing what those things are supposed to be used for, having open and polite discussions with one another. Trade stories of previous RPs in threads about amusing adventures/tales you've written with others, play the forum games and show your unique brand of humor, and present good-natured, polite, well-articulated arguments and counters in the public debate forums , and you'll get at least a few people who'll say that they like you as a person and want to establish contact. There's also the practice of joining RPs and, by bonding over the act of writing a saga together, creating friendships with people you're attuned to writing with.
This last part is coming more from a tabletop gamer point of view, so take it with a grain of salt in terms of if it applies to you. As a tabletop gamer, be careful about using Roll20 to create tabletop groups and calling everyone in said groups your friends - while Roll20 is a wonderful site and tool for facilitating tabletop gaming online, there's a distinct population of oddballs and never-do-wells that will pop up in nearly every listing, asking to join a game. Not going to name names, just be aware that sometimes, people might be lying to you about others on there or trying to take over the whole show from both the GM and the other players. Generally, what I did while using Roll20 to find players was join groups, establish friendships with the people I meshed well with as players and out-of-game as just general acquaintances to hang out with, and after the game ended for whatever ended (a lot of games end on Roll20 prematurely for a variety of reasons; GM or players might get hit with stuff IRL, the group might realize a GM is incompatible with how they play tabletop game, personalities just don't mesh with well, or, worst of all, a player/GM actively working in the background to set everyone against each other), I'd keep in contact with the players I enjoyed the company of and, through them, make contact with even more players like them and me. Networking is pretty key in finding fellow roleplayers, especially when you're just hanging around on Discord or somewhere, not sure of which servers or threads might be for you.
There's also the possibility of attending conventions and hobby stores for tabletop roleplaying, but... well, I haven't had the good fortune to attend either due to living in a part of the United States where there isn't a hobby store reasonably close by and same with conventions. I will say that, based on what evidence I've heard in discussions with those who have attended said events/stores, conventions tend to get you a greater variety of people since the convention itself might be a wider topic such as comics, science fiction, fantasy, or just general pop culture, so you get a good mix of new players who bring a fresh flair to the game and experienced players who know how to run and play a character in the game you're playing without much encouragement. Hobby store wise, you generally have a pretty older/experienced crowd attending them, which can be both intimidating as a new player/newcomer to the start or very welcoming as if they're nice folks willing to help you learn the game. They can introduce you to established groups with games that you can join in as well - however, just a precaution, be wary for the more... out there members of a community, or for just a generally toxic store. While the vast majority of stores are well-run with a fairly polite crowd, almost every store also has one troublemaker who for various reasons is tolerated but considered a ponce by the wider community, and sometimes, you get lucky and are stuck with an entire store of toxic individuals or a store run by a manager who isn't quite all there. If you go to a hobby store, mind your books, sheets, dice, and if you're there for wargaming or card games, your decks and miniatures until you know for certain that the people you're associating with are decent.