did Miyauchi turned into omega?? or s.th like that/?

no... LOL where did you get that idea

so does male betas can give birth? because i read in one of omegaverse mangas that if you bite beta he can turn into omega. or if a alpha forced to live like omega he will evantually turn into omega

Pretty sure its bc alpha's "seed" is alot more stronger/dominant. Beta's are hard to impregnate but once an alpha is in 'rut' they have a higher "seed count" which could impregnate a beta.

that's not the rule of this omega-verse. The only "set" rule of omergaverses is that alpha is the strongest, omegas is the weakest, and alphas and omegas are fated couples. Other than that, the author decides how the omegaverse works. In this case, everyone can get pregnant, no matter the gender. Betas are harder to impregnate than omegas, so they have to make it up by quantity.