A few user reported that they were not able to connect with Excel. It was installed and opened but still the popup came up saying it cannot be found. We broke this issue down with the reportings of a user (thanks, Kevin).
It seems to only appear if Excel is installed from the AppStore. This (somehow) corrupts the launch database of macOS – or in other words: If MyDataMerge asks macOS for the app, macOS answers “No there isn’t any”. As we are forced to use Apples methods to work inside their security universe we cannot bypass this.

So our recommendation is:

Download the desktop app from the Microsoft 365 Website (login here: https://m365.cloud.microsoft/) and click the button top right “Installation and more”. Then download the 365 installer and from there install Excel locally. Do not forget to delete the AppStore App before (Drag to trash, empty trash).

This should make it work.

Regards
Pat