The iPhone “XR” could not be synced because the sync session failed to start.

That happens to me as well from time to time. I have never gone nuclear. Usually restarting the iOS devices and restart iTunes works for me. If that fails, I reboot my Mac and restart the devices again.

I’ve had that happen occasionally both with iPhones as well as iPads when ‘iTunes-ing’ them onto a Mac. Went nuclear, which fixed the issue every time: on the iGadget did a Force Restart (link for iPhones) and Force Quit all apps, on the Mac restarted it, went into Recovery Mode, ran First Aid in its Disk Utility, then Reset the NVRAM and booted in Safe Boot Mode, before restarting normally and retrying.

Your mileage may vary and need not go thru all these.

Hello,

See this:

If your computer doesn't recognize your iPhone, iPad, or iPod

Good luck.