Garmin should really embrace this. The alternative, relying on smartphone apps, will lock them out in the long run. The big advantage of buying dedicated hardware, like a Garmin bike computer, is having more control over your data.
I expected some synergy but I got nothing. When monitoring the same activity with the two devices you just gets dupes (for example, sum of the distances measured by the two devices). This is worse than if I had 2 devices from 2 different brands.
FWIW you might have been looking for extended display mode.
https://support.garmin.com/en-US/?faq=fZaD0E9cTwAwBffjoJcWT8
There's another related defect if you use one of their chest straps that records and stores heart rate data for later download (this is mainly for swimming activities where radio can't be used). If you record an activity on your watch and it syncs to Garmin Connect before downloading heart rate data, then after the watch downloads from the chest strap it will create a duplicate activity in Garmin Connect instead of updating the existing activity. Customers have been complaining about this for years but Garmin doesn't care.
On e.g. files that are uploaded from my Garmin watch, Strava adds its auto pause as a filter on top of the data: iff the original data doesn't have any pauses (Garmin auto pause not enabled on my runs), then Strava will cut out periods of time when you're standing still; otherwise it'll leave the data alone.