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Open Settings → Apps & Notifications → Special app access → Install unknown apps. Select your browser and enable "Allow from this source".
Tap the download notification in your status bar, or open File Manager → Downloads and tap the .apk file.
Tap "Install" when prompted. After installation, tap "Open" to launch the application.
"App not installed" — ensure unknown sources is enabled and you have at least 100 MB free storage. Delete the old APK and re-download.