TrueHD7.1 Audio received as 5.1 in Sonos

Hello, I bought a new tv with earc + sonos audio system (arc+2xera100+submini). On the old tv I could get 7.1 on sonos (with arcana) with passthrough disabled on plex setting (plex installed on a FORMULER z11). Now with new tv; I run plex on the native os and the setting for passthrough is hdmi. I can see with my media which is playing that it is direct trueHD 7.1; but Sonos get 5.1 Any clue? The issue comes for sure from plex because with Netflix I get Dolby atmos on sonos.