There were a handful of successful online PS2 games. SOCOM and FinalFantasy were 2 but there was another called EverQuest Online Adventures (EQOA). That game was shut down in 2013 and there’s a group of former players that are trying to resurrect it. The main way to play what is left post-end of life is using PCSX2.
https://www.projectreturnhome.com/