Muso Hekla confusion

So, I’ve had my Hekla for a week.

Very happy….However….

Using an Apple TV 4K, through SamsungTV audio on pass through, I am never fully confident that I am getting atmos.

On the app it show atmos and I can change the audio mode and it changes. When I go into audio settings, hdmi, and change the mode it doesn’t change the sound, but when I go into PCM stereo and change the listening mode, the audio mode does change, atmos music, sphere etc.

How can I be sure I am getting genuine atmos?

Is the TV the problem?

The Apple TV?

Just general hdmi handshake issues?