Yes, you are right. To be honest, I haven't bothered about the background colour yet, because it's very easy to change afterwards. I decided to use the light blue from the stripe of the C64 logo - all other colours look too aggressive... But I have noticed something: All platform videos in my category "Computers" now have a light blue background: Windows, MS-DOS, Amiga and now C64. Is that okay, what do you think?
I think this is where I come to the end with my Photoshop skills ? I must note that the monitor is not a separate layer. The whole setup is a bitmap. So when I apply the lens Correction, for example the floppy drive becomes skewed. I have therefore tried the transormation mode, where you put a grid over the image and can bend individual nodes (unfortunately I don't know what this is called in English). And unfortunately I can't do that perfectly... It's difficult without a pen, only with a mouse and without a steady hand. Please see attached screenshot.
I still have one question: The videos are to be compressed with VidCoder - that's clear. But which export settings do I use in After Effects beforehand?