Mac OS: No signal via HDMI over RallyPlus?

Hello!

We are facing the problem of not getting a signal from our Apple products via RallyPlus to the display.
Although the computer recognizes the external screen and adjusts the resolution, the external screen still shows that there is no signal available.

Suspect 1: The USB C to HDMI adapter is guilty. Unfortunately, the same situation was also present with an Apple computer with an integrated HDMI port.

Test-wise, we connected a Windows computer, which immediately created a transfer.

Any solutions or experience in this regard?

Many thanks!