Factory bluetooth can work
I figured out why my factory Intel 9650 bluetooth that comes on the ASUS Z390-i would seemingly randomly work.. then not work.
Windows! If had booted to Windows, and rebooted into Catalina, the bluetooth would work.
If i powered down my pc, bluetooth wouldn’t work from a cold boot into Catalina.
I suspect this is something to do with how the firmware works - windows loads it into the RAM of the Intel card.
I then tried installing a more permanent kext, and this one here seems to be working so far for cold MacOS boots
https://github.com/OpenIntelWireless/IntelBluetoothFirmware
No handoff or airdrop, but i’m using it with bluetooth speakers and a Magic Trackpad, and working well.