So, Apple has stopped supporting to backup my iPhone on my macOS?

I have iOS devices that are kept at the latest versions. I have macOS machines that currently still run Mojave and for the time being cannot be upgraded.

When I connect my iPhone, I now get "A software update is required to connect to [name] iPhone". What is unclear to be if that is an OS-update (so I'll get booted to Big Sur which I do not want) or if it is just a component.

What is clear to me that — as is — we can no longer backup our iOS devices and company policy forbids backups to iCloud. In effect: no more backups. That worries me.

So is it indeed the case that the 'update' is a full macOS update? Or is it just the update of a component (which I do not expect or it would have been part of a regular patch).