I've been looking for an online game like these kinds of manhwas but can't find any 😿

Like a manhwa with an online game plot or an actual online game?

If it's the actual online game i can suggest a few:
Ragnarok Origins Global
Maple Story (start up is slow if youre f2p tho)
Twin Saga

Here are my recommendations!

Flyff Universe, you can play this entirely in browser so it's nice on the go
Mabinogi, very active community with tons of quests
Maple Story, if I had to guess this is probably what Illusion is based on since it's a very popular Korean MMO that's been around for years

Twin saga is no longer on steam, I used to frekn love that game and now it's gooone :'(

Oh right i forgot they rebranded(re-opened?), they're called Astral Tale now

I don't know the status of the game now as i've stopped playing though, but I did check and they are still on steam

I play Ragnarok Online on mobile! New costumes come out every month! And there's a guild system with guild wars and various events!