I think it's the Whitestone Dome protector that most recommend.
Whitestone Dome Film. It has the same feel as the factory (PET), better adhesive and better at resisting dust and fingerprints. Under $20. Watch some videos on installation before going for it. It's not hard if you take the proper care and time to install.
https://smile.amazon.com/Whitestone-Premium-folding-Protector-Anti-Bubble/dp/B09LV4WKCM
I agree with _Bob_A_Feet_, liquid to hide scratches and a tempered glass for the outer screen.
For the INNER screen, go with this: https://smile.amazon.com/Whitestone-Premium-folding-Protector-Anti-Bubble/dp/B09LV4WKCM/ref=sr_1_3