Ok, to check it, I did this:
and then I restarted it manually with a modified config in /etc/mosquitto/mosquitto.conf containing this:
by doing this:
mosquitto -v -c /etc/mosquitto/mosquitto.conf
The broker replies with
Error: Websockets support not available.
which is the typical answer when the websockets function is not compiled. So, all there would be needed to do is to compile the already available option into the mqtt package. Is somebody from teltonika reading here to maybe add this feature to the roadmap?