if you playing on mobile especially old ark, u need prime jerky, longrass, rex egg, mejoberry, water, and fire it with sparkpowder in cooking pot. congrats now u have rex kibble in ark mobile.

One male can reproduce with multiple females simultaneously, so get 1 male and a ton of females, that way you get fert and normal eggs. + because of the fert eggs, you have a better rate of getting eggs to make kibble.

If you can, search for a female rex and tame it. Much easier to get eggs rather than follow her around

You can tame one then let them mate and then watch until it lays then after that you can get so much more