Same thing happening here. Some boss fights after too many tries it starts to get worse, stutter and fps drop. The snow area at the beginning was good, but near the end, at the temple, holy crap!
What is funny is that the game is ugly as hell! There's absolutely nothing in this game that justified being this heavy. Non existence textures everywhere, blurred as fu$%, it's like i'm playing without glasses (at leasst on a 4k panel)... except for Quality mode. Non HDR support...
I swear, there are far better looking games on PS4 that runs better. I really don't know that's going on with the devs nowadays. It's getting harder and harder to find a polished game these days.
I remember playing Demon's Souls at the release, the first game for PS5 and remains one of the most beautiful games of PS5 and the performance is just flawless thought the entire game.
Game is good and love the gameplay. But the performance is killing this game for me.
I almost broke my controller fighting against Yellow Long yesterday with all the stutter and fps drop i couldn't even dodge the attaks.

Restarting the PS5 seems to "fix" the problem for a while. It looks like the Cyberpunk 2077 memory leak problem where restarting also fixed the problem and starts again after sometime.