Hi ArekSkomur,
Can you provide us with some additional details please?
Please provide your specs including OS, CPU, RAM and GPU model.
Also, if you know the user you are trying to connect with can you give us the same details about that player (including if they are on the Epic or Steam platforms) and also the general location of both players.
Have you tried to join with random players via online matchmaking?
If so do you get the same result (SYNC WORLD 0%) for everyone or just specific users?