Before you diagnose anything: open the extension's own autofill settings and look for an option along the lines of display suggestions when the icon is selected.
When that is switched on, the suggestion menu no longer opens when you click the field. It opens when you click the small vault icon inside the field. From the outside that is indistinguishable from "inline autofill has stopped working", because the thing you have done for years — click field, get menu — now produces nothing at all.
Switch it off, click a username field, and you will know within five seconds. It costs nothing and it is reversible.
Why this one is so widely misdiagnosed is the part actually worth taking away. Look at your list: reinstall the extension, clean profile, disable the browser's blocking. Every one of those targets state stored in the browser. An extension setting like this is attached to your account and syncs down, so a fresh install pulls it straight back and a clean profile arrives with it already applied. The three most obvious tests all quietly reproduce the cause instead of eliminating it, and each clean result pushes you further towards blaming the browser.
That is also why these threads get so long. The people who happen to have the toggle on and the people with a genuine browser problem describe exactly the same symptom, so the reports pile into one place and neither group's fix works for the other.
If the toggle is already off, then you are in the second group and the rest of the answers here apply.