After installing Postgres from official installer you’ll soon notice a new user on your Login screen, “Postgres”, to hide it perform the following:

sudo defaults write /Library/Preferences/com.apple.loginwindow HiddenUsersList -array-add postgres

After your log-out and login again you won’t be presented with that user, to reverse this change do:

sudo defaults delete /Library/Preferences/com.apple.loginwindow HiddenUsersList

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