I gave it another go with the hint above about the tetherd log:

  tail -f ~/.local/state/tether/tetherd.log

I was then able to see and pair over wifi and bluetooth. Everything is enabled except Notifications (even though both address book sync + notifications are enabled in iOS bluetooth settings).

Clipboard sync working now as well as send/receive files.

The tether app still has occasional issues re-connecting to tether though when I move in and out of the app.