I am the most, very most stupid man in the world....
I cannot believe it myself...

I was following Jacek's tip and opened Screen prefs. Okay:
Ambient - RadeonX1650 24Bit 1920 x 1080.

BUT: After I wanted to edit that, there were only modes for the HD5450!!! :((
First I thought: ohhhh, there went somethong wrong. MorphOS does not correctly recognize my gfx board any longer...and the second thought was: Is the X1650 actually installed...???

NOOO!

Some weeks ago I did some tests with different gfx boards (HD5450, X1650, X1950 Pro/XT) and finally - please do not ask me why - I did not install again the X1650, which was the goal (watching YT videos!!!!), but the HD5450.

So embarrassing!

Please apologize!

The best: Not only YT works with Wayfarer, everything is so much faster.
MorphOS developer: PLease support more current gfx boards. It is such a difference.