Since none of the solutions found here Silencing "Your disk is almost full" notification worked for me on Mojave, I simply disabled the daemon:
sudo mv /System/Library/PrivateFrameworks/StorageManagement.framework/Resources/diskspaced /System/Library/PrivateFrameworks/StorageManagement.framework/Resources/diskspaced.disabled
Brute force, I know, but unloading/removing/disabling using
launchctl didn't work and I got annoyed.
Is there a more elegant way to turn off Apple's constant nannying alert messages?