As far as your update goes, I believe this is the first incremental update from Onyx.
That's presuming that the small size is not because of an aborted download.
Did you decrypt it before you tried to do anything with it?
Did you manually put the strings in DeBooxUpd.py?
Could you do a listing of the decrypted version?
It should only be 20 lines or so.
Code:
C:\>7zip l update.zip
If you can find the "META-INF/com/google/android/updater-script" and "update-binary" please extract and post just those files.
Use fastboot getvar all and look at what your active slot is.
Then post the recovery that came from that slot.
To make a custom recovery there is a bunch of stuff that needs to patched.
I have to look closely at this because you've got an A/B
Hey! There's a new "Tab X"?
https://shop.boox.com/products/tabx