I have gotten Thunkable to connect to micro:bit before like yourself, but once connected, I could not get sending and receiving data to work. The project was a boundary device, meaning the micro:bit was attached to, for example, a person. The device would beep if they left the premises by constantly checking for loss of Bluetooth signal.
Unfortunately I could not find great documentation with micro:bit and Thunkable (being combined) to get all my Bluetooth Characteristics UUID and things like that. I am sure it is possible though.
This is definitely something that could be better documented
What are you trying to do? Could this be achieved without Thunkable? What kind of data are you sending? I found that if you use serial with Raspberry Pi or Windows machine, that you can just use Firebase with a Python script to communicate data with multiple devices.