I think it's the tempered glass protectors. The TPU protectors seem to work fine. I'm using this and haven't really had any finger print problems. Also installation was super easy.I don't think I've read a single review of screen protectors for the Pixel 6 / 6 Pro on Amazon where buyers haven't said that the finger print sensor doesn't work when they've applied theirs.
Looks like the only option is to run a naked screen...
As an Amazon Associate, MacRumors earns a commission from qualifying purchases made through links in this post.