Why does my Web App’s “Add to Home Screen” prompt not show on Android, even though the PWA criteria seem to be met?

I’m trying to make my web app installable as a PWA on Android.
The app loads fine, works offline, and Lighthouse gives me a passing PWA score.
But the “Add to Home Screen” prompt never appears on Chrome for Android, even after multiple reloads and usage sessions.

What I’ve done so far

• I added a valid Web App Manifest (name, icons, display mode, theme color).

• Service worker is registered and caching works correctly.

• Site is served over HTTPS.

• Checked Chrome → chrome://flags to make sure nothing is disabled.

• Tried uninstalling old versions of the app from the device.

• Browsed the app for several minutes to trigger engagement heuristics.

Main Problem

Even with all this in place, the install prompt never shows up.
Is there anything else Android/Chrome checks before showing the “Add to Home Screen” banner?
Could it be related to user engagement thresholds, start_url issues, or something else I'm overlooking?

Any guidance would help as I’m stuck trying to figure out the one missing piece.