Installation on macos 12 fails

I have a rather old MacBookAir running the latest macOS 12 w/ Adobe Acrobat Reader installed:

Since a few days, trying to update (via the “Help” menu) fails with an error, so I decided to simply re-install it.  Therefore, I downloaded the installation dmg, but running it fails with

The box is running 12.x… Any idea what goes wrong here?