Thanks, I have tried the optical output connected to a Bluetooth transmitter. Unfortunately the Sonos soundbar hijacks it away from the optical output too. No dual output.  
 

I could connect the the TV to the soundbar using the optical cable, but then I’m not sure what would happen to the Atmos surround sound, i assume the remote control would still adjust the volume, but some other functions might be lost. Any thoughts on that? 

Likewise for a Samsung TU8000 and an Arc.  With Anynet+ enabled, the Bluetooth headphones will connect and be disconnected instantaneosuly.  As frustrating as it is, it is part of the CEC/HDMI.  My solution was simply to disable Anynet+ unfortunately.

Surprisingly, this issue has been there for 2+ years and it’s still there. I just bought an Arc yesterday (5/2/2021)and got problem with my Bose headphone being hijacked after few seconds.

Someone said due to spec of CEC/HDMI bla...bla. and turning off Any+net, ... Then why Samsung HW-Q800A/ZA soundbar has no such problem? The Samsung soundbar also connected to TV via the same wire and same port (eArc), why it allows me to switch among TV Speakers, Headphone, and Soundbar seamlessly?

I like Arc sound more than Samsung’s, but I have to return the Arc due to this annoying problem. I use headphone a lot at night, so I can accept this issue. Blaming on TV doesn’t make sense because others  can produce theirs soundbar with the same technology and have no such problem

Pretty much the same than ppl statement - in 2021, product designed without basic interaction capabilities that compete product allows without further tweaks is a down vote on the market. I’ll return my Sonos Arc for other compatible product that could allow a seamless experience across devices. Cheers.