Linux Player only shows black

Hello everyone,
I have the following problem.
The Xibo CMS (4.1.2) runs on an Ubuntu 22.04 LTS server. It works well. I also have Ubuntu 22.04 running with the Linux player on the client. I simply installed the player via snap (1.8-R6). The connection between the CMS and the player seems to work in principle.

My problem, however, is that the player does not display any content. Apart from images (jpg, ping, etc.), only a black screen is displayed. I have already tried using Ubuntu version 24.04 LTS, without success. The CMS in an older version 3.x was also unsuccessful. A further attempt with a Windows client showed that it works.
I hope someone here can help me get the system to work on a Linux basis.

Many thanks.