How to stop receiving "iPhone software update" notifications on my mac

User wrote " I'm working with several different iPhones with different iOS versions every day." it would seem obvious - let the OS be updated for the iPhone. Apple pushes updates for iPhones for a reason.

Once the offending iPhone(s) iOS is updated - the annoyance notification will cease.

Came across this, do not know if this will help your situation but maybe. Receive, pause, or stop notifications on Mac

One must a Good Reason not to update the iOS for whatever reason - Developments etc. Then am a a loose to offer any more assistance other than not connect iPhone to computer or run the update bit that is not a solution for your purposes.

Good Luck and maybe a more Senior Contributor will pickup the thread