They're still using UE4 for FFVII Rebirth (albeit a modified version of it) so maybe with the 3rd part if they switch to Unreal Engine 5? And only if that one will be made from the ground-up for the PS6.
I remember reading from one of the info dumps from late last year that they'll be using UE4 that's why I mentioned it. That said, it's so fucking weird that I can't find a real source anymore. Even the wiki page itself mentions UE4, but there's no actual source behind that info.
Best I've found is from a rando video a screenshot where Naoki Hamaguchi is saying they'll be using UE4 still but heavily customized version of it.
I’d love the third game to switch but I’m sure that throws massive wrenches into the production pipeline and they’ve already stated they are into part 3 development.
John Linneman noted before that the geometry looks to have a nanite kind of look to it so he wasn't sure if it was UE5 or UE4 previously, but now we basically know it's heavily modified UE4. I think it's becoming clearer that these consoles can't make the most of the UE5 full feature set without compromises, so I don't think there'd be much to gain visually from developing it on UE5 vs a customised UE4. The engine they've crafted has been engineered to make the game look and play how the developers want it to, so I'm not expecting them to switch to UE5 for the final part.
That said I could see an FFX Remake being developed with UE5 for PS6.
if it's the 1st part of the remake - the good parts had too many boring side quests with PS3-looking NPCs as quest-givers? Like damn, why are they stretching a remake into 3 parts, people don't hate tight focused games last time I checked...