The behavior of the internal keyboard of the MacBook Pro differs from that of the external Mac Bluetooth keyboard

I have a Swiss German Keyboard (Internal and External Mac Bluetooth Swiss German keyboard)

grafik

On the top left corner you will find the § sign.

When I press this on the internal keyboard, this will recognized and translated from BTT correctly.
When I press this on the external keyboard, this will not be recognized from BTT and my application seems to receive a "5" instead (at least it does the same as when I press the 5).

Btw. This text is written with the external keyboard, and you see it deliveres the § correctly.

MacOS Big Sur 11.1
Macbook Pro Late 2016 with Touchbar
BetterTouchTool 3.551

In general BTT just takes the input the system gives to it.

Does the key behave correctly on both keyboards when BTT is not running? If not possibly the wrong keyboard type has been selected for the external keyboard, in that case possibly run the initialisation in System Preferences again:

As I told before, I wrote this text with the External Keyboard.
That means the Keyboard deliveres the correct Sign when I type §.
I also reconfigured the key within BTT with use of the external keyboard
to check if BTT receives the § correct.

wait then I don’t understand. If the keyboard works fine without BTT and BTT also recognizes the key correctly, what doesn’t work exactly? The assigned action?

Yes, the app seems to receive 5 instead of Ü
It's very strange