HI Henk,
The tutorials have a watermark from “post-production”, as the UI is not really an option for rendering other than with screen capture software.
If you like to have it in your renderings, use the Render-Settings>Effect>Watermark.
If you would tell me more what you like to do, e.g., record a tutorial, then I have perhaps more specific information.
For temporal use: Perhaps not really the question, but you could always load an image into a material and open the image in a new window and place this into the interface as any other UI frame. See image. It might not be a stable solution for UI switching, though.
I typically record uncompressed or lossless compressed. Placing a logo into it, might cause problems later on, if the logo changes or any other compression is needed. So, for me, it might be in post anyway.
My best wishes