Video / Dark bar at the bottom

Happy New Year to you all! Gutes Neues Jahr!

I get a dark bar across the bottom of my videos. The original does not show any dark bar. It also doesn’t show in Sparkle directly but it does in PREVIEW.

When I use “Browser built-In” the dark bar is gone. BUT! I don’t like that design too much. I rather like it as modest as possible.

Has anyone had this issue and knows how to fix it? Many thanks in advance!

Kind regards

These are my settings (screenshots)