iOS App Store Connect Sales and Trends show "Desktop" users We recently noticed, through our App Store Connect Sales and Trends page, that our iOS app has some confusing statistics. Our app shows that we have Desktop devices in our metrics.

Although iOS apps can now be made to run on macOS, we have explicitly declined/disabled that feature (at least we think we did...) for now both in the Xcode build and in the App Store Connect availability.

The phrasing is a little confusing to me. The checkbox mentions Silicon/M1 devices explicitly, but I thought Desktop compatibility applied to (potentially) any macOS device on Big Sur. Either way, it's unchecked!
Further, none of the App Store Connect analytics seem to show that we have Desktop device entries for our users/units. Only the &quot;Sales and Trends&quot; page shows any Desktop data.
This is befuddling. How could a Desktop analytic event have gotten in there? I'm willing to accept it's some weird fluke, but also want to make sure we're not missing something and a certain subset of macOS users are somehow able to run our iOS app.
It seems that your declining the macOS option is administrative only. It does not prevent people running your .ipa on their M1 Macs, so long as it's running under the correct Apple ID.
To do this you need to extract the .ipa from the phone to the Mac, using iMazing.
From The Verge, a quote from the makers of iMazing

App management has been available in iMazing since November 2017. We did not do any particular adjustments to ensure that iOS apps exported from iMazing’s library would run on Apple Silicon Macs. It turns out that when developers choose whether or not to include their mobile app on the Mac App Store, no change is made to the app itself – the setting is purely a distribution toggle.