Can I remove this thing from ‘Look Me Up By Email’? This app was uninstalled long time ago and it’s still showing on all my devices.
This is just a residue in the look-me-up list.The app does not have access to refreshing the list when it is uninstalled on your devices. We do have forwarded this issue to Apple’s dev team about this issue and hopefully, it could be fixed eventually.
A couple of words about this if what you are actually concerned about is your privacy protection. The feature is added in MarginNote 2 given that app supports sharing an exported notebook to a fellow MarginNote user so that some sort of teamwork can be achieved. It serves only this purpose and no more than that. Plus, ticking it off in the list is already an effective measure to turn it off for good.
To sum up, it is a left-over option that can be turned off and will not affect your (un)using of your macOS device.