Where to allow it: Settings → Apps → your browser → Install unknown apps → Allow from this source.
Play Protect may warn because this build did not come from Google Play. Tap More details, then Install anyway — that is expected.
Xiaomi (MIUI/HyperOS): if the install is blocked or stalls, turn off Security's "Scan apps before installing", and allow your browser under Settings → Privacy protection → Special permissions → Install unknown apps.
Updating? Just install the newer APK over the old one — no need to uninstall. The app can also notify you when a new version is out.
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