No sound from the TV?

But so far I am only an invited user who does not invite himself. Nevertheless, I have a request or a question. For weeks I try to transfer the sound and the image at a conference on a TV, because especially the sound is terrible from such a mobile phone and dS image too small to make with the exercises. I can't manage to transfer the sound. The sound from e.g. Youtube is always transmitted. But as soon as Zoom is on, the TV goes silent and the sound comes out of the tablet. Is there an explanation for this? What am I doing wrong? What is the solution? I have already tried the following: 1. notebook (win 10) with HDMI cable to the TV 2. tablet No. 1 Samsung (Android 5) with screnn mirrow to the TV 3. tablet No. 1 with HDMI adapter to the TV 4. new tablet (Android 10) with new HDMI adapter to the TV 5. new tablet with miracast adapter to the TV It's always the same with Zoom Picture yes, sound no. Can you help me there please? Many greetings Klaus