Macbook Pro Bluetooth not available after plugging in a dongle
This seems to be a general problem with motherboards of 2019 models.
Check this link:
https://discussions.apple.com/thread/250944058
There are many people including myself that has this problem.
It seems like the only resolution to the problem is a motherboard replacement.
I have exactly the same error and problem.
I used a dongle that supports mac.
Just for information:
I have tried to reinstall, clear t2 chip using xartutil --clear-all, nvram reset, smc reset and so on.
Seems motherboard replacement is the only resolution.
Update: A new method to fix this problem has been revealed on the apple forums: https://discussions.apple.com/thread/250944058