now I have reinstalled my whole system and I changed to CGX4. I added a new 320x240 8bit screenmode and looks good when I test this mode (look at attachment).
I donīt know why but by starting ScummVM rtg it always stops. In the error.log is an entry "Couldnīt switch to mode 320x240 (bit)" and in 320_240.mode contains a line with 1074921472.
I can use this screenmode at the workbench. I also can open both splash screens in the scummVM package.
Any hints what I could still try?