I am ... stupid ...
As always, the problem sits between monitor and keyboard.
After I built both the Legacy DWC 1 and the current Master Branch and also the DEV3.2 Branch of DWC, I had to get the SD card.
And what had I seen? In the folder GCODES there was another folder GCODES ...
So the files already ended up correctly in the folder GCODES, which I mistakenly considered as ROOT. Now that I have removed the DEV3.2 and have equipped my SD card with DWC 1.x and 3.1.1, and have created the GCODES folder anew, I can now proceed as desired...
Silly me.
It is just too warm at the moment (34°C)
Greetings and thanks
MoS-tekknix