After several weeks with endless research and testing I succeeded.
My Galaxy S10+ is now on /e/OS 1.6 S !
The /e/OS community was very very helpful 
My fault was to first update my device to the latest stock ROM-version.
So the solution was to downgrade:
- At samfw.com I got the Spanish firmware AMO G975FXXSGHVI4 from September 2022
- I flashed it with Odin 3.14.4
- After reboot I activated developer options, USB debugging, OEM unlock
- Then Odin again: I installed twrp-3.7.0_9-0-beyond2lte.img.tar (in AP) and vbmeta.img.tar (in CP)
- And then followed this brilliant Howto at step 8)
- After reboot finally the dancing “e” …
Many thanks to everybody