My iPhone is set to back up to iCloud but it backs up to my computer whenever connected

I don't want my iPhone to backup to my computer. I have it set to backup to iCloud in the phone's iCloud settings and I have plenty of free space on iCloud. It automatically backs up to iCloud every day like it's supposed to.

However, whenever I plug my phone into my Mac to sync media, the 'Backup to This Computer' setting in iTunes switches on by itself and a wired backup begins. So I switch the setting back to 'Backup to iCloud' and re-sync and again it switches to 'Backup to This Computer' on its own. In other words, iTunes keeps overriding my settings from the desired 'Backup to iCloud' to the undesired 'Backup to This Computer.'

All devices are fully updated and this has happened with 2 different iPhones and on 2 different Macs. I don't want to erase my devices and set up them up as new if I can avoid it, so any other troubleshooting suggestions would be greatly appreciated.