I am going to respectfully disagree, I think if you have a desire to learn and participate everyone can have fun online in fighting games. Don’t get baited by thinking that you need to learn all these combos and moves and be 100% perfect at doing it all the time. Cause you dont.
The difference between someone just starting and a pro is vast, and will seem daunting and like you need to know a bunch of stuff. But honestly competitve starts out similar to you and a bunch of pals just having fun together.
You are playing the other person, getting reliable damage from a combo is more important to begin with than doing optimal damage. For street fighter(it is what I have the most experience with), you need to know how to anti air to stop people from jumping(this is usually a crouching Heavy Punch, but can be different for some characters). Then throw in a simple combo, can be an easy target combo(or using the modern inputs in SF6) or something as simple as HP > Fireball/Tatsu. And then making sure you know basics like blocking and throws, drive impact and drive parry for street fighter 6.
That seems like a lot, but it is less than the mechanics of most single player games that get thrown out in tutorials, and the rest of the knowledge will come with time and practice. Say you come across someone who just cleanly wipes the floor with you, you can look at the replay and see if there is a gap, or learn the timings, or if it is unsafe if you just kept blocking. But that won’t be something you have to worry about for a while. You will spend a lot of time figuring out how to handle people randomly throwing out DP or Drive Impact or who just won’t stop jumping.