Software update is required to connect your iOS device. What is the update?

I connected my iOS 13 phone to my Mojave Macbook and received a message saying software needs to be installed (see: https://support.apple.com/en-us/HT208831)

Can someone tell me WHAT software would be updated and to what? Is this going to upgrade MacOS from Mojave to Catalina (I don't want that quite yet)? Is it going to replace iTunes (I don't want that quite yet)? Or is it just going to update iTunes?