I found a better solution. I use private listening. I installed the roku apk on my fire 7 2019. Then I turn on private listening. Then I pair my jbl everest 700 headphones to that. And walla. Just leave my tablet plugged in all the time.
The posters on this string miss the point of my original post. When I bought my Roku/TCL TVs, each of them could connect to any BT device directly without adapters, apps, or other work-arounds. It was not until February of 2020 when Roku issued a firmware "upgrade" did I lose that functionality. If I bought my TVs today, knowing that I could only connect directly to Roku proprietary devices, I would have no complaint. But that's not the case. Roku removed the functionality I purchased without my consent.