Hi, I am still learning the inner works of the Teltonika routers - find them very confusing compared to say pfSense or Cisco.
I have been wondering about the same question - so far found, that the live graph of traffic does indicate which WAN connection is being utilized (WAN/mobile 1 / Mobile 2).
The Interface status will show WAN + one Mobile as active, so not much help - but the graph -when you look at bandwidth usage - clearly tells you if data is flowing over WAN or Mobile