Geto most certainly had a domain expansion
Geto 100% had a domain expansion in canon, based on three main points. I am aware that DE did not exist in JJK 0, but people seem to (rightfully) accept that gojo would have had a DE at the time of JJK 0, and I am using that same logic to apply to Geto.
Story wise, Geto is seen as the second strongest character in jjk at the time of jjk 0, and it makes sense for him to have the strongest move in jjk.
Kenjaku’s DE. We see that when yujo uses DE, he uses gojo’s DE instead of his own, which means that when using someone else’s body, the domain you use can be the domain of the person whose body you are inside. Further, the person may even be forced to use that body’s DE (possible but not confirmed). This, coupled with the fact that kenjakus domain is made of many faces (curses?) and references wombs (like Geto swallowing curses and keeping them in his stomach), suggests the DE may be getos.
Although this is completely hindsight, if gege had came up with DE before jjk 0, a logical reason why Geto would not use a domain against yuta at the end of jjk 0 is that doing so would make him lose control of all his curses, meaning that he has two scenarios. A, he kills risk and yuta and thus his purpose for going to yuta fails and gojo kills him shortly after. B, he kills yuta but not rika, which is great because he can now grab rika except he can’t use his CT and gets killed by rika and possibly even his own curses.
The biggest issue with my theory is that the CT in kenjakus domain seems to look more like gravity BUT that’s not confirmed AND if Kenny used gravity in the domain he may have lost it and would have been unable to use it against the blonde baddie AND the domain looks more like curses than gravity.