I play music on my Google Home Hub through an external Samsung Bluetooth speaker. The initial pairing has to be done from Google Home app, but after this, it's sufficient to say "Hei Google, connect to Bluetooth" and Google Home would say "OK, looking for paired devices" and almost immediately connect to the speaker. This worked absolutely fine for around 6 months and then suddenly Google Home Hub instead of connecting to Bluetooth would respond "Sorry, power controls is not yet supported..."
I was trying to modify the command in various ways without much success, until eventually, I said "Hey Google, turn on Bluetooth" to which Google Home replied "You got it, turning the Denon on" and promptly turned on my Denon receiver. Now, this was quite bizarre... I have Logitech Harmony linked to my Google Home, which allows launching various Harmony activities and devices via voice commands. I double checked all activities and devices and none of them had word "Bluetooth" in their name. No idea why suddenly word "Bluetooth" started triggering Denon AVR.
Anyway, after a bit more experimenting I found that command "Hey Google, enable Bluetooth" was a good workaround. I use this now instead of "...connect to Bluetooth" and it works as expected.
March 2019
Google Home Hub
Logitech Harmony Elite
Denon AVR-X2200W
