iCloud Tabs no longer a feature in Safari 13?
I noticed this problem a while ago, but didn't dig into it until now. I am using iOS 13.3 and trying to get tabs from 10.13.6. 

The Apple support page clarifies what should work and what will not work:


  iCloud Tabs works between devices running iOS 13 or iPadOS and macOS
  Mojave 10.14.4 or later, or between devices running iOS 12 or earlier
  and macOS Mojave 10.14.3 or earlier.


Apple's What's new in the updates for macOS Mojave page does not mention changes that would make things incompatible, but here is a much more detailed break down of the 10.14.4 update.

So:

Catalina &amp; iOS 13 - iCloud Tabs should work

Mojave 10.14.4 &amp; iOS 13 - iCloud Tabs should work

Any version of macOS less than Mojave 10.14.4 won't work without iOS 13 for iCloud Tabs.

If you're running iOS 12, then don't go above Mojave 10.14.3 or you will not have iCloud Tabs anymore.