Followed your advice @Pin255 and Bixby Voice Command is now updating.
I'm in the UK.
All updated and it's added.
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 2.5/ Android 10.
You seem to be missing the point. You don't hold the button when you say "Hi Bixby". Bixby works on my Note 8 when I hold the button, but trying to set up "Hi Bixby" it just continually says it can't hear me.