Sorry, why would someone want to play the PS4 version if they have the PS5? Is it a save file issue not being usable on the PS5?
Why would you want to play a PS4 version when there is a PS5 version of the same available?
I have Mortal Kombat and if I'm playing online, I much prefer the PS4 version because the DualShock 4 feels much better to use. If I'm just having the AI grind towers, I'll run the PS5 version for loading. Both have their save info on WB's server, so the important stuff is not lost.
But we wouldn't need to keep a PS4 version around if Sony hadn't blocked DS4 use in PS5 games for no reason other than selling more DualSense controllers.
There are also multi-player games where people have extra DS4s but don't want to be forced to buy multiple $70 controllers just for local play sessions. In
this thread, we have people defending this bonehead policy saying, "just play the PS4 version if you want to use the DS4". So, those are a few reasons.
Ideally, we shouldn't want to, but Sony's handling controller support poorly.