i finally installed successfully the EU Version Rom …
here are some remarks how to install the ROM before you going insane 
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after you unpacked the zip and rar files, shorten the folder names, the driver software and the flashtool cannot proccess the long filenames with the chinese characters.
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installation of the MTK driver fails ? search google for “how to deactivate driver signature enforcement”
once the driver signature check is disabled, you can install the drivers - otherwise it wont work ! -
everything is in place but nothing happens ?
check your USB cable ! its strongly recommended to use the original cable which came with the tablet - many aftermarket cables are not fully capable of datatransfer - it took me just 2 hours to realize that
the android 11 update makes the Tablet much more responsive - i had a very early version of this tablet , even received one OTA update before , but it was always a bit laggy, now very much useable and much snappier and faster responses …
also google security updates working now … just got the latest android 11 security update from google.
the upgrade is really worth it!
good luck everyone