I too have been unable to load the companion app to my iMac running the most current version of Big Sur. I am not using an M1 Mac, so the problem may be related to the Big Sur OS. I have tried both the pkg and dmg versions of the Mac download and get the same error each time.
Here is the message:
“net.downloadhelper.coapp-1.6.0.pkg” can’t be opened because Apple cannot check it for malicious software.
This software needs to be updated. Contact the developer for more information.