i’m confused, how’s this MPreg but he’s a beta?

Maybe he'll change

There are Omegaverses out there that if the alpha is a dominant alpha then the partners secondary gender is irrelevant when it comes to pregnancy. And vice versa. Which is what I’m assuming happens here.
Otherwise he’ll have to somehow suddenly become an omega, which is a pretty common trope amongst the Omegaverse genre.

He's blessed by the fairy king, he'll still be a beta but he'll be able to give birth

Well.. omegaverse has many variation...

There's omegaverse that make the omega and female the only one who's can pregnant...

There's also omegaverse that make everyone can get pregnant, even alpha male x alpha male and omega male x omega male or even beta male x beta male, or alpha male x beta male, etc.

There's also omegaverse that make the omega and female the only one who's can pregnant, plus only dominant alpha can get every gender pregnant, even though the opposite is beta..

I don't know which one this manhwa was ..