No more Bluetooth-LE on Raspi ?

[Alf-Gordon]

Hello,
I want to use Raspimatic on Homeassistant OS 6.6 Installation on a Raspi 3B.
I think it would be best for me to use the GPIO HM-MOD-RPI-PCB for communication.
The installation-guide told me to edit the /mnt/boot/config.txt
First : I can't find that file, because my mnt-Folder is empty. Do I have to create this folder and file ?
Second : It told me to uncomment Bluetooth.
My problem is that I need BT-LE for my Xiaomi Mijia Thermometers in Hassio, and I do have a lot of them.
Maybe I misunderstood the exlaination.
Thank You for hints.

Greetings
Alf-Gordon