I'm chiming in here because I'm having the exact same problem as Tony. During my first week with this MoBo (X570 Creator) I could even use the Intel BT OOB, no AirportFixup etc or other BT patches necessary. Then, one day, it just stopped working. As the onboard AX Wifi didn't work anyway, I bought a Fenvi FT-919 combo PCIe card. Installed it, used the MoBo USB-Header for the BT connection. Wifi and BT worked OOB with all the good stuff, Airdrop, Handoff etc.
Then, after a couple of days, BT stopped working again!
As with TonyZ, I saw the BT symbol and the BT device correctly shown under system info, but wasn't able to connect devices. I thought this was happening due to an incorrect USB mapping so the internal USB port was somehow omitted. After using @CaseySJs XHC SSDT, I can finally see XHC, XHCI and XHC2 and I thought my problems were solved because BT worked again, for several days (including shutdown and reboots). Today, I switched on the
machine and BT doesn't work AGAIN! I tried experimenting with all the available BCRM patches but with no result.
One thing I noticed: I'm using Apple keyboard and mouse. When the Fenvi card is working correctly, I can use these devices during boot for the OC picker and within the BIOS, so before any OS gets loaded. But during some boots, I'm unable to use the keyboard via BT and that's exactly, when there is no connection happening in MacOS. Does this give you a clue @CaseySJ? I think this was the same with the internal Intel BT. To me it seems that the MoBo doesn't enable BT "legacy support" (can't remember what it's called) correctly during boot and therefore, MacOS can't use it..
Regarding the TB issue, I can use TB for my TB3 Drobo 5D3 but without hot-plug of course. I found a guide which explains how to patch the BIOS with the AMIBCP software (Windows needed) to show more options in the BIOS for Thunderbolt to enable hotplugging, but unfortunately the software doesn't show ANY Thunderbolt options to activate at all. I'm still investigating.
BTW @CaseySJ you're really doing some great work here, thanks a lot! Any way to support you somehow?
While the BT doesn't work, IOReg only shows a generic IOUSBHost device and not the full name Broadcom etc etc... edit: actually, this is not entirely true. The BT controller shows up correctly in IOReg, but no device connects. After clicking on the BT icon and turning BT off and then on again, IOReg shows the generic device.
edit: Signature with build info attached, picture of IOreg attached
Ok, this is weird.. I just noticed, that AirDrop actually works. I'm still unable to connect BT devices like keyboard, mouse or AirPods. As AirDrop works, Bluetooth MUST work somehow, because AirDrop uses BT to locate devices that are close and initiates a connection to create an adhoc wifi network which then transports the files.