Last modified: Sat May 16 2020 14:57:16 GMT+0000 (Coordinated Universal Time)
So with Bluetooth in macOS, it can become quite confusing on what actually is supported and what's not.
Well I was orginally going to manually find every supported model but user MarkVillacampa has done a great job already so I'll link to his findings
Asus and Lenovo note: On 7th gen and newer chipsets, Bluetooth has been intergrated into the PCH and these OEMS don't have any USB rails wired off of their A/E slots. This means that you'll need to either solder new headers for Bluetooth on your motherboard or route a USB cable to an existing port
Well, it's a bit complicated and involves looking at IOkit and how it handles different devices. Bluetooth is actually quite simple in how it interacts with the system and thanks to being generally run off the USB rail, generic devices can easily hook into IOKit and act semi natively(usually with the loss of Handoff, Airdrop, etc). Wifi, on the other hand, is quite a bit more complicated as there needs to be explicit support in the IO80211 family for the device so only Broadcom/Atheros cards have any chance of working
So if you rebooted from Windows into macOS, the firmware on the card may have stuck on allowing you temporary Bluetooth support on your'stve card. To make sure this sticks around, you can use a firmware injecting kext like that found on the IntelBluetoothFirmware repo
So to support Bluetooth in the BIOS, you'll need a Bluetooth device that supports HID Proxy. The idea of HID proxy is to create a minimal Bluetooth stack that is then used into tricking the BIOS into thinking your Bluetooth keyboard is actually a USB one, as there aren't any firmwares that actually implement Bluetooth.
All of Apple's cards natively support this feature but you'll need to search on a case-by-case basis with other devices
This is mainly for devices that only have 1 Bluetooth profile which can be a bit frustrating when switching between OSes, we'll our local Frewt boll has saved us again!