Hi Cedric,
According to the wiki here:
https://github.com/cedricp/ddt4all/wiki/Android-port
I downloaded and installed the latest version there (DOWNLOAD LINK V1.9) -> EcuTweaker-1.9.apk
And it seems this particular version has a bug which leads to problem with connecting to bluetooth devices:
when clicking on Select device button (in bluetooth mode/icon) nothing happens (bluetooth persmission has been granted).

When I downgraded to previous version: EcuTweaker-release-v1.85.apk then all is working just fine.

Maybe this bug was fixed in the mean time (sorry for reporting then), I only want to report this, so you are aware of this problem.

Tested on: Galaxy A10 / Android 11