According to Microsoft's document on SFS, SFS and PRT are the same thing. PRT was created about a decade ago by id's John Carmack, but was pretty much only used in their 2011 game Rage from what I'm reading. It works by breaking down a scene into tiles, and then the texture quality needed for each tile is determined by the distance from the player to the tile, so that for each tile, you only need to have a single texture loaded into the RAM, instead of having all possible texture resolutions for the entire scene loaded into the RAM at once, so that they can be accessed as the player moves through the world and texture quality settings change based on distance.

The main difference seems to be that Rage's implementation of PRT used CPU resources to decide which tiles need which texture resolutions, sapping a good bit of CPU power. This article from Microsoft seems to suggest that Series X has dedicated hardware for SFS built into the GPU, freeing up CPU resources. Not sure if PS5's GPU will have similar functionality, or if devs on PS5 will need to use CPU resources for PRT.