Works for some things. Check the neighboring directory, LaunchDaemons, for additional culprits. Found disturbing items there from apps never used. Apple claims to police security - how did this stuff all get in there?
Still cleaning these up doesn't stop all notifications. Also check, as noted above, Settings/General/Login Items.
The most elusive appears to be Spotify. I get this kind of notice regarding Spotify, but there are no entries from Spotify in either of those directories. Actually, no file or directory with Spotify in the name anywhere on my hard drive. But, in Login Items, there is an entry for Spotify, which I have turned off. Where is this bugger?
Frustrated, I search for .plist in Finder. Great googly-moogly. Over 1000 finds. 305 app.data (these all from Evernote, which I do use, invoking plists), 174 .tagset (these seem mostly to be related to Apple music, also invoking plists), remainder a balance of plists and .h files (from SDKs, etc.).
tagsets (whatever they are) have cryptic names (e.g. 000000b0-00000000-45424147.tagset), app.data are named only that, plists have vague names (e.g. SystemVersion.plist) as do .h (e.g. SMErrors), not transparently associated with apps.
To identify, I put Finder in list format, observed directories displayed at the bottom of Finder.
Threw away one plist from Google. I don't knowlingly let Google on my machine, but they are elusive.
No sign of Spotify.