Final Fantasy XVI / 16 was officially revealed in September 2020 during the PS5 showcase with an epic trailer. Not much is yet known about the game however from the trailer, it appears to be returning the series back to a medieval fantasy setting in a much more mature way with actual blood and horror-like themes.
After Final Fantasy 15's problems, some of the most requested features from fans are a better open world, more polished (and perhaps new) battle systems, and a much larger focus on a surreal, epic, and cohesive story. It seems Final Fantasy VII Remake has them in the right direction regarding battle system and story telling but the bar has never been set higher for the next majority installment of the franchise.
Final Fantasy 14's director Yoshida is the producer for Final Fantasy 16 and according to journalist Jason Schreier, it won't be too long before we'll get to play it as Square Enix has reportedly been working on this game "in some capacity" for the last four years. More information (and hopefully gameplay!) is set to be revealed in 2021 but no release date has been announced as of yet.