The performance hit seems to be worse on lower end systems like steam deck as you can see in the vid as there's about a 10-15fps difference, sometimes more.
Even in higher end rigs there seems to still be a 10-20fps difference as you can see in this video with a 4060ti.
On the RE subreddit they were saying if you were using DLSS4 injection or other mods they don't work anymore too.