Other than making sure you have system notifications turned on for the Target features, there isn’t much you could do to troubleshoot this from the Scrivener side of things. How loud they are, whether they appear, whether the Mac is in “do not disturb” mode—all that stuff is in System Settings: Notifications.
Also, if you have recently started using composition mode more often, do be aware that in its default setup it is meant to put the system into a kind of focus mode, that shuts down notifications. I.e. you want to focus on your writing and stop getting the Discord and mail notifications—but that incidentally takes down your Scrivener notifications too! There is an alternative setting you can use, described in that thread, that should dodge that problem, but then of course you get distracted again by other notes.