Online friend groups are created more through repetition than anything else. Literally just joining a discord and be there at the same time every day brute forces you into a friend group. Honestly I think a lot of offline friend groups are created through this repetition also, a bunch of people sharing the same interest on the same schedule often becomes a friend group of convenience. The thing with online is that you tend to get out of it what you put in, if you're invisible and lurk you don't gain recognisability in the group and don't tend to do stuff with other people as a result of being considered an active group member. This also kinda requires the group to actually be doing stuff too though, and some of them definitely don't.

I can never seem to make friends online or offline

All my online friends I have through Discord. Can't really help much beyond that, it's just kind of developed from regular contact over extended periods of time in shared spaces. Definitely helps when the space is a bit smaller though. The downside to it is that it can feel kinda fragile (at least in my experience). Like there have been a few moments (although fewer than you might think when we're all leftists lol) where a couple of my friends have gotten into a bad argument and one of them just leaves the sever, which at least for me makes it kind of hard to maintain things with them just because I'm not great one on one with people online.