0.13.6 High Sierra Mac OS won't sync with iPhone running 14.6

Perhaps try to make settings across your products, so they may work together?

• Use Continuity to work across Apple devices - Apple Support

//support.apple.com/guide/mac-help/work-across-devices-with-continuity-mchl1d734309/10.13/mac/10.13

• Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

//support.apple.com/en-us/HT204681

• System requirements for Continuity on Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

//support.apple.com/en-us/HT204689

.The word "sync" may mean more than one thing, depending on circumstances.

• If your computer doesn't recognize your iPhone, iPad, or iPod - Apple Support

I'd not used that to describe non-communication when continuity was involved.

PS: Was there a reason for not updating your iPhone's iOS to 15.5?

That should be most compatible with many systems; & work best.

My iPhone SE (1st edition) has iOS 15.5; it works well enough

plus the main desktop Mac here, runs High Sierra 10.13.6 OK.

The reference article above this thread, has items of interest.

..What the other factors are behind the total situation there.?