It can be legal to race a prototype for such a race (but maybe not for the Olympic races), as long as it is declared to World Atletics as a development shoe.
The list is update regularly. Access here (first item in “manuals and guidelines”, you can download the full list, dev shoes highlighted in blue):
https://worldathletics.org/about-iaaf/documents/technical-information
The Altra Vanish Prime (now called Vanish Carbon) development shoes was valid roughly all 2021 (as per october 21 list) but it is not anymore in the list (I guess it is one year only). So, indeed, not sure it is legal now until official launch.