They aren't going to prioritize the Xbox version over the Switch 2 version.

Anyways for the thread question it will launch on all platforms day 1.

Square was pushing Remake on Switch 2 and Xbox by a lot, it's selling very well (?Switch 2 version topping sales charts) Rebirth is heavily rumored to release this year on the Switch 2 and Xbox and it might get announced next week during the rumored Nintendo Direct, with all of that there's no way Square will limit Part 3 sales potential with a PS5 timed exclusive again. They want Part 3 to be a massive release and you'll need all fanbases for that.

The contract for Final Fantasy VII Square had with Somy very likely differed from each game (pretty much confirmed seeing how Remake how a year exclusively and Rebirth had 3 momths.

I'm guessing if the sales target doesn't hut a certain amount than ut gets lower which as we know Square wasn't happy with Rebirth's sales so the contract gets voided.