The receiver doesn't have any preouts whatsoever. The only way to feed any audio to headphones is to use Zone 2. This is also going to be required because the audio coming into the receiver will be in full surround sound, while the receiver will downmix the surround sound audio to stereo for zone 2.

If you already have zone 2 hooked up to another room, then you are out of options.

This is something I have given a lot of thought to over the years and have come to the conclusion that if people want to do exactly what you want to do, you need to dedicate a second/third zone for this specific purpose. All manufacturers that I've seen do things this way. There is not a single good solution from ANYONE I've seen.

I do strongly suggest that instead of Bluetooth which introduces latency to the audio and isn't really meant for real time video, you should get some wireless headphones.

My in-laws and several family members use the Sennheiser RS-120s.
https://www.amazon.com/Sennheiser-RS120-Wireless-Headphones-Charging/dp/B0001FTVEK/ref=sr_1_3

I have provided these to many clients as well.

This is very much a 'you can't get here from there' scenario as the ONLY way to preserve surround sound is to let the A/V receiver downmix your audio to the second zone for you and use that feed for the headphones. You can program a universal remote to turn on zone 2 and zone 1 at the same time and track the same source easily.

In my home, I use very expensive downmixing equipment to preserve my surround sound mix as well as give a stereo feed which I can then use for my headphone connections. It would be cheaper for you to buy a new receiver with more zones if that's what you needed to do over what I've chosen to do.

You can't use a HDMI audio extractor because it doesn't have any integrated DSP. That is, the audio would need to come into it as 'stereo' to get stereo out for a set of headphones. This is a huge issue because you would lose surround sound.

May I ask why you don't use the Zone 2 output? This really is the best solution as the A/V receiver can process surround sound to stereo for zone 2 while keeping surround sound in the main zone.

You get a RCA level output which you can feed to a proper set of wireless headphones like I linked, or try that Bluetooth transmitter unit which you linked. You may find the audio delay with Bluetooth to be intolerable. But, that's up to you.