This project turns your generic ESP32 board into a natively supported USB Bluetooth dongle!
It works by running the ESP32 as an HCI controller and exposing its UART interface to the computer.
Assuming you are running bluez (check systemctl status bluetooth, there should be something running),
connect your ESP32 board, flash this project via idf.py.
Then, check what tty the board is connected to, for instance /dev/ttyUSB0.
Lastly, you need to connect to the board, running hciattach -s 921600 /dev/ttyUSB0 any 921600 noflow.
You can check if the device was connected to by running hciconfig, there should be one device like this:
hciX: Type: Primary Bus: UART
BD Address: C4:4F:33:11:3B:B3 ACL MTU: 1021:9 SCO MTU: 255:4
UP RUNNING PSCAN ISCAN
RX bytes:138145 acl:90 sco:0 events:15057 errors:0
TX bytes:12237259 acl:14383 sco:0 commands:223 errors:0
Look for Bus: UART.
From that point on, bluetooth should work in your OS.
When you want to stop using the thing, run killall hciattach.
If you reset your esp, it might get tangled up in the OS. In that case, run sudo hciconfig hciX reset.
well, no idea, really...
Ideally you need an HCI driver that talks to a HCI controller through a COM port...