If I can recall, there was a manga I read with an Enigma. They're basically the peak Alphas in the alpha world who are capable of mating with other alpha and making them bare child.
However, the child baring was very sudden.
Realistically, how the Enigma would work is that they will pour in pheromones on their alpha partner. The body of the partner will register the enigma pheromones and will go through a transitional process (not the alpha to omega kind) which allows their body to bare the Enigma's child. Like an instinctual thing where the strongest genes must be passed on no matter what. Because of that instinct, the dominant alpha genes will HAVE to bare their child. Heck, they're even the optimum birthing choice.
The Enigma would have to constantly pour in their pheromones onto their partner in order for the partner's body to constantly have the chemical trigger to activate the transitional process. If they were to cease abruptly, it could have consequences on the partner because their body, which was preparing a birthing chamber that was never supposed to be there in the first place, lost the chemical trigger to continue. Their body would have to deal with an incomplete foreign organ that's purpose is not completely defined. It could cause pheromone, hormone, psychological, and neighboring organ malfunctions.
So, unlike the manga I had read, the transitioning process should be much longer. Perhaps 1-2 years (depending on the individual's health).
So to sum it up, the reason why Enigma x Alpha cases work is because of the ABO instinct to pass on only the strongest genes. This allows their seed to grow regardless of secondary gender. And yes, it's their pheromones, because it triggers the transition.
I hope this will help you sleep.

So off topic, but; how can an Enigma, like taejus dad get an alpha pregnant? I was trying to make up a fake scenario in my head but now I can’t get over who the hell Ts works… like is it the pheromones or what. Someone please help me.
I will not be able to sleep until I get answers