Almost every failed installation fails for the same reason, and it is not the protector. A single particle of dust — house dust, lint from a sleeve, a fragment of the old protector — sits between the adhesive and the panel and holds a pocket of air open around itself. The bubble you see at the end is that pocket. No amount of pressing removes it, because there is something solid under there.
Which means the whole job is preparation. If the panel is genuinely clean when the sheet goes down, the adhesive does the rest by itself: it pulls outward from the centre and any small perimeter bubbles clear within a day. If it isn't, you will be starting again.
Do it in a bathroom
Run a hot shower for two minutes, then leave. The steam pulls airborne dust down out of the air and settles it, which gives you the cleanest room in the house for about ten minutes. It sounds like folklore and it is the single most effective thing on this page.
Clean in three passes
The alcohol pad lifts oil. The microfibre cloth lifts the alcohol. The dust sticker lifts what the cloth left behind — and it will have left something behind, because a cloth pushes particles around as much as it removes them. Hold the phone against a light at a shallow angle to check; dust that is invisible face-on shows up immediately at 20 degrees.
If you find a speck after the sheet is down, lift the glass from one corner with tape, remove the particle with the sticker, and lower it again. The adhesive tolerates two or three lifts. It does not tolerate a fingerprint, so hold the sheet by its edges.
Let it fall, don't press it
Seat the alignment frame, peel the backing, hold the sheet level over the middle of the panel and let go. Pressing at the edges first traps air in the centre with nowhere to go. Dropping it flat from the middle lets the adhesive spread outward the way it was designed to.
Then leave it alone. Perimeter bubbles smaller than a grain of rice are adhesive still wetting out, and they close on their own within twenty-four hours.