Updating again ...
I have a TV and a monitor. I always turn on one or the other, never both.
I want both to show the same so I have selected the "Unify Outputs" in the Display Configuration (Meta + P). If I select just one of them and change when needed, there are stability problems like "Desktop Effects switching off", so that's why I select "Unify Outputs".
The Monitor is selected as Primary. The TV never shows the Oxygen splash screen, but the Monitor does, so it seems "Splash Screen = None" only applies to the TV. This is strange because the TV is not the primary output.
I have tried all combinations in these values. All of them have problems, some bigger than others.
The configuration I have now, just have this small problem with the splash screen.