Reddit user DasVergeben leaked it last year, as part of a larger
post:
A month later he
mentions that the developer was MediaVision and that the game was in development for PS4:
It is known that MediaVision is working on a RPG exclusive to the PS4 since 2018 thanks to a series of job listings. Also, if you recall ZhugeEX's comments on ResetEra early last year, he mentioned that a couple of unannounced PS4 exclusives based on existing IPs were made cross-gen releases or moved entirely to the PS5. The new Wild Arms could very well be one of those titles.
In addition to this, we know that MediaVision has been growing their staff count a lot during the last year or so.