I'm not entirely convinced that save data will transfer between FFVII remake entries. I hope it does, to make it feel like a more cohesive "single long game" once all parts are released, but I feel like it's going to start over as pseudo-level-1 just with a more powerful "base level" to reflect the experience gained in the first game.
I feel this is especially likely given that it's apparently a bit of a headache to transfer the PS4 save data for it to the PS5 version... you basically have to install the PS4 version before you get the PS5 version, go into the game menu, upload the save to PSN, quite, completely delete the PS4 version data, THEN get the PS5 version, and download the save from PSN. If you do it in the wrong order you can't downgrade from PS5 version to PS4 version to access the save file
.
So... it's not been designed in a way that particularly has me thinking they'll be carrying over the data. The vast majority who played part 1 on PS4 simply won't have access to that data on PS5 (which presumably, most people will be playing part 2 on, if there even is a PS4 version).