If you create a microflow to be accessed solely from a URL (i.e. what would have been a deeplink in the past), it is listed when you search for unused items from the 'Find Advanced' option and doesn't show any usages if you click on 'search for usages'. This might make it easy for someone to accidentally delete it when cleaning up the app or when working on an older application.
It would be better if it showed up in the results with the element of 'called from URL'. Since the default is for microflows not to have a URL, any with a URL defined is probably intentional.
That does achieve it, though I still think the process of setting a URL indicates it's use as much as adding a button to a page (if not more so as it usually involves more effort), so why not include having a URL set as part of the definition of 'used'
You can set "Mark as used" to prevent microflows from showing up in unused item search results.