Calendar Sync Problem on a Single Device

OK, so, here's the gear that's involved:

• iPhone 12 Pro Max running iOS 16.4.1(a)
• iPad (8th Gen) running iOS 16.4.1(a)
• iTunes for Windows 64-bit 12.12.7.1
• PC running Windows 10 Pro, Build 19045
• Microsoft 365, including Outlook Version 2304 (Build 16327.20214 Click-to-Run)

Here's the problem: I can no longer sync my calendar from my Microsoft Outlook to my iPhone through iTunes.

I know that calendar sync has not yet been deprecated for iTunes 12.12.7.1. That is confirmed here. Yet, I have not been able to sync my iPhone calendar as of today.

I tried everything I could think of: upgrading iTunes to 12.12.8.2; switching USB ports; switching USB cables; rebooting my iPhone; rebooting my computer; uninstalling iTunes 12.12.8.2 and reinstalling iTunes 12.12.7.1. I even considered downgrading from iOS 16.4.1(a) to plain vanilla 16.4.1. (I didn't.)

Nothing works so far. During the process it does indicate "syncing calendar", and then "copying items", but then the calendar items simply do not show up on the phone's calendar.

But then here's the thing: I just plugged in my iPad, synced that, and the calendar items do show up there.

So it looks like it might just be the phone itself.

Can any provide any troubleshooting tips that can help me solve this?

Thank you.