Risk of Rain Returns (after its released, since youve already played RoR2)

Gunfire Reborn

Deep Rock Galactic

Escape from Tarkov

Valheim

Terraria

Minecraft

Maaaaaaaybe "Stardew Valley"?

If you dont mind a F2P with Pay2Progress and some borderline P2W Mechanics, "World of Tanks" maybe?

An online party of Anno (1404, 2070 or 1800)? They can go on for long, but pretty much everybody has to play at the same time.

Maybe either DayZ or the DayZ Origin Mod of Arma 2?