Syncing iPhone 17 Pro Max to MacBook Air fails

Thank you for taking the time to reply.

Previous backups with older iPhones using iTunes on my older Macbook Pro did not present any conflicts even though these were different Apple accounts. But considering that Apple may have changed the way things work with syncing, I went ahead to create a user account for my husband on the Macbook Air and signed into his Apple account, then plugged in the iPhone, after switching it to airplane mode and deactivating auto lock.

However, syncing failed with the same error as before: 'waiting for changes to be applied'. The message flashes by so fast that it's scarcely readable.

As for your advice to upgrade to Tahoe, that shouldn't be the issue here at all. Sequoia ought not to be the problem with syncing the iPhone. FYI, I make it a practice to hold off on upgrades until a number of software updates have been released resolving bugs in the earlier releases.

I welcome any further suggestions you may have.

Initially sync was stuck at step 2, 'calculating'. A search for this issue turned up reports from users who discovered that switching off their Apple watches or otherwise switching the iPhone into airplane mode enabled the process to move forward and complete the sync.

Ordinarily when plugging in the iPhone to the MB Air and opening it in Finder, the option for backup defaults to iCloud. This is no longer the case. Now, every time the backup to this computer is selected - even after countless restarts. I wonder if this has any connection to the error 'waiting for changes to be applied'. Why doesn't the backup option revert to the iCloud default? Is there some way to kill it in Terminal?