I struggled with this nonsense for a week and almost came here to see if there was logical chance of fixing it.
Every other App played over Bose Bluetooth just fine except YouTube.
Just by luck I stumbled on this setting and it blew me away how hidden it is on the Note20Ultra.
Switched it to Bose vs phone and now YouTube is back on the speaker.
Oddly enough even though speaker was connected and touching controls on speaker can stop YouTube video, but absolutely no sound was possible.
Talk about a mind bender, and at seventy, patiently losing it was on the edge. To initially thinking it was the speaker.
Pretty sneaky stuff Samsung.
