I updated to to macOS 11.3 (Mojave) a few days ago. This morning when I connected my iPhone (via USB) I was prompted to install additional Mac software in order to access my iPhone (from iTunes - although iTiunes was not open). This might have been associated with the security update that I installed yesterday ( Security Update 2021-002 Catalina and 2021-003 Mojave - #4 by andkim1974 ).
There was no explanation of the extra software update - just a prompt to install it.