I received a 75 in Q94a tv yesterday. It's connected to Samsung Q90r soundbar, which is plugged into HDMI SOCKET 3, FOR eArc.
I started the on-board Disney+ app and Netflix app. Both apps display Atmos in the description, next to 4k/HDR, but the sound coming from the soundbar was just Standard on both apps. Soundbar displayed eArc. I closed the apps and tried again, but sound description on both apps had reverted to 5.1.
The HDMI ARC option is now greyed out on the tv set.