Quickly wear the face of the devil? Edit: I think I that has a similar world, the third or fourth world he went to? Can't remember exactly, need to re read it.
https://www.novelupdates.com/series/abo-cadets/ A little bit similar, but its seems not u are looking for since MC and ML not transmigrated But it does have MC who thinks he is beta but he is a omega
There is one called Its Actually not easy being the supporting male lead they are both "actors" tied to a system. The MC is a "newbie" with no rights, while the partner is someone who has complete control of the system.
Hmm, that sounds familiar. It might have been a spoiler thread I read a while ago? Tagging @alexfilia who is the Queen of all BL
https://www.novelupdates.com/series...tagonists-with-delusions-of-starting-a-harem/ Actually, the novel under omegaverse is only a few, maybe u should just look the tag https://www.novelupdates.com/stag/omegaverse/