Thank you, version 30.0.5 worked for me. I have now a fully functional /e/OS running on my GS290. Thank you all for your assistance! And special thanks to Gigaset for the software repair of my device.
By the way, where can I find the sha256 checksums for the recovery image on this page?
https://images.ecloud.global/stable/GS290/
I only can find the checksum for the system image.
Why does the fastboot process not work the current fastboot version? Is this a failure in fastboot
or in the /e/OS images? Should this bug be reported to the fastboot maintainers?