I have resolved the issue by re-installing indi-libgphoto2.
Now my camera is no longer detected as "PTP class camera" but as "Canon EOS 80D" instead.
Now triggering the shutter and capturing images with gphoto2 works flawlessly both in "Bulk" or "Manual" mode.
In KStars/Ekos the camera is now connected and I'm asked for the sensor resolution. After input of sensor resolution
I can trigger liveview and capture and download images.

Works now like a charm !

Thanks to all for your suggestions!

Clear night skies!

Helmut
Cologne/Germany

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