JonBek actually. This has changed recently. I’m watching only and my HR data gets synced, along with my GPS and speed. I also recently recorded a 5h walk with HR and no phone being present.
This is my bike commute from today (watch only).

Hilariously, if I start recording with the mobile app, I get a double event with GPS and HR going to Strava.
See here:

Also, while this recent update now works perfect for events with GPS data and no phone present. The happened in parallel with the phone-only Strava linking working well.
YES!
However, I can’t share my non-GPS stuff (indoor rowing) to Strava any longer and my workaround has broken sadly. This also occurred with the recent update.
I usually record a morning kettlebell session, two bike rides and a lunchtime rowing event daily now.