Something else, perhaps? If we have Blokada 4.x or 5 installed from F-droid, even if not activated, then don’t try to upgrade or change version, without uninstalling the original version first, or it simply won’t install. The OS message simply says unknown error, presumably meaning a fingerprint error where the installer doesn’t recognise it’s a different version? At least it seems to be the case on vanilla Android 10, but at least all my original settings, including Plus, automatically came back on the fresh install, without the need for reconfiguration.
Sadly from experience it seems the original version might not uninstall properly, so it might be necessary to reinstall and uninstall the original version again before trying to upgrade again. A pain, but it’s worth it!
A strange thing too is that it seems only v4.9 will install when no other version will!