iTunes in Mac doesn't recognize my new iPhone when I connect it

Don't rush into an OS upgrade just yet. High Sierra should work. See if you have any iTunes updates waiting first. Install any iTunes updates before doing a system upgrade.

Did you get an advisory like the one shown in this Apple article:

If you see "Software update is required to connect to your iOS device" on your iPhone, iPad, or iPod touch - Apple Support

If so simply accept the update. It does not change you Mac OS level. It only applies a small patch to enable iTunes to continue to manage, sync, and backup your phone as before.

Yes… update your MacBook Pro to El Capitan or Mojave. Your iphone 12 needs iTunes 12.8 or better to work in your Mac… El Capitan is available here, likewise Mojave. Please use Safari with this link for best results:

https://support.apple.com/en-ca/HT211683

john b

Are there any AntiVirus, Disk Cleaner, Optimizers, Unistallers,etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation.

Per chance - is " CleanMyMac " installed as it will fall into the above outlined Category and should be removed as per the Developers Specific Instruction.

My iPhone 6S isn't recognized by iTunes (ver. 12.8.3.1) on my iMac running High Sierra, ever since updating from iOS 14.4.2(i.e. it was recognized @ 14.4.2).

Additionally, the Photos App however, does recognize my iPhone 6S (with iOS 14.7.1).