Hey there big_smile,
It looks like you are concerned a number of Apple apps may not continue to sync between your iPhone and Mac if you update your iPhone to iOS 16.
You'll be good to go.
Taking a look at System requirements for iCloud,
"iCloud requires an Apple ID, an active internet connection, and up to date software. If you meet the recommended system requirements below, you can take advantage of the latest iCloud features and get the best overall experience. To see the minimum requirements for each feature, you can review the minimum requirements at the bottom of this page.
To use iCloud, you need at least iOS 5 on iPhone 3GS, iPod touch (3rd generation), iPad, or iPad mini; or at least OS X Lion 10.7.5 on a Mac.
Reminders (upgraded features)
Reminders is available on iPhone, iPad, or iPod touch, and Mac.
- iOS 13 or iPadOS
- macOS Catalina
Notes (upgraded features)
Notes is available on iPhone, iPad, or iPod touch, and Mac.
- iOS 9
- OS X El Capitan 10.11
iCloud Drive
iCloud Drive is available on iPhone, iPad, or iPod touch, Mac, and PC.
- iOS 8
- OS X Yosemite
- Windows 10 with iCloud for Windows 10 or later"
Have a good one!