Some don't fit correctly I agree @Mickey1121
Some only have adhesive along it's edges which means they can pop off, and some are not very case friendly.
There are quite a few that adhere to the phone's display with silicone which is an option I use.
My choice > The Whitestone Dome Glass Screen Protector adheres all over the screen and is fingerprint scanner friendly and works with a multitude of cases.
The Whitestone Dome comes with a plastic cradle that you sit the phone into and then from some further steps the phone adheres to the phone and it comes with an ultra violet light that cures the silicone underneath creating a sealed result.
There is instructional videos both on Whitestones website and on YouTube.
Now this isn't a cheap option but in my own personal experiences of using different glass screen protectors it's the best available.
I wish you all the best with your choices.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.