I created my app on a Mac (OS 11.6.1) using Python 3.9 and the pyinstaller package. I was able to go through the notarization and stapling steps okay. Moreover, typing
spctl --assess --type execute -vvv '/Users/fishbacp/Desktop/dist/main_app.app'
resulted in /Users/fishbacp/Desktop/dist/main_app.app: accepted source=Notarized Developer ID origin=Developer ID Application: John Doe (XXXXXXXXXX)
I tried to launch the app on someone else's machine (OS 12.0.1) after unzipping it. The icon bounced around in the system tray for a few seconds before disappearing.
If it helps at all, the app runs fine on my machine, but the icon appearance changes after a few seconds from what I chose it to be to the python matplotlib icon shown below: