Running the 8.4.0 installer on W10 22H2:
The installer says digiKam is running - but it isn’t. Continuing by selecting “Ignore” starts de-installation of version 8.3.0. It reports a successful de-installation. Moving on again the installer says digiKam is running. After a restart the installation succeeds.
Not a big problem, rather a nuisance. The digikam bug tracker has no category for installation. So I posted it here.