eOS (GSI-version) on Doogee V20 Pro does not start

I would like to have eOS on my Doogee V20 Pro.
As there is no dedicated version yet, I was hoping to be able to flash the GSI-version.
By using treble, I found the right “system.img” and I could also flash it, but after flashing, eOS does not start. It goes immediately into the fastboot mode.
Do I need to flash further files? Or change some settings by any command of fastboot?
Maybe I have a similar trouble as described here:

but I have not yet the original Doogee stock ROM files. Doogee promised to send them to me soon, so hopefully I can try to re-flash “boot.img” and make the “–disable-verity”-step.

Regain your privacy! Adopt /e/OS the unGoogled mobile OS and online servicesphone

If your Doogee is running stock Android 12 or A13 - /e/OS-Q GSI (Andrroid 10) may not work.

Only use GSI images with an Android version that is higher than or equal to the Android version running on your device.

The files boot.img and vbmeta.img can be dumped on the running system, for example with MTKClent via python (Linux Ubuntu, ArchLinux, Windows).