[2023] What Happened? is it illegal?

Hi! I'm playing thru Steam (PC) I'm level 100+, and I bought a brand new Steamdeck week ago from a store for my birthday to play outside. Downloaded FO76 on steamdeck and it's my first game on the device obviously, I tried to play on the steam deck and it was smooth. 2-3 days after they banned me for "Cheating and/or Exploiting via the usage of a third-party program". I used StreamLabs OBS (Streaming application for PC) because I did a share my gameplay on Facebook since level 15. So my question is Streaming the game thru OBS illegal? or playing thru steamdeck is illegal? and the Agent and support can't explain any detailed information about what I did wrong.

Thank you for answering/helping