How exactly do I play online?

[Velineon]

I've updated to 1.16.4 and now, every game I attempt to join it says something about an "Out-of-Sync Error" I am not able to join any games, due to this being the problem on all of them. I tried some of the possible fixes, such as deleting any mods and that wasn't the case. The game is literally like new, nothing has been changed...I reinstalled it once and it didn't do anything.