iOS App Store Connect Sales and Trends show "Desktop" users
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.