@peterbault
Your question is really a Sony issue (or that of any TV manufacturer) and not Sonos. Below is the official word from Sonos regarding audio reproduction by the Arc for any TV:
Sonos Arc can connect to TVs with eARC, ARC, or optical outputs. For greatest compatibility, eARC is recommended.
If you connect to a TV with eARC, the Dolby audio formats supported include Dolby Atmos, TrueHD, MAT, Dolby Digital Plus, and Dolby Digital.
If you connect to a TV using ARC, the Dolby audio formats supported are dependent on your TV model and manufacturer. The TV may be capable of sending Dolby Atmos, Dolby Digital Plus, and Dolby Digital. An ARC connection cannot support TrueHD or MAT.
If you connect to a TV using the optical adapter, the Dolby audio formats supported are dependent on your TV model and manufacturer. The TV may be capable of sending Dolby Digital. An optical connection cannot support Dolby Atmos, TrueHD, MAT, or Dolby Digital Plus.