You have to be aware that there are now two versions of the 3.4.2b-1206 being used for the Mi 10 (umi).
1. There is the one that is now being included with the weekly ROMs. This one does not decrypt, so to update the weekly ROM installations, this might typically be done using USB-OTG. This has advantages over the previously used LittleTurtle version.
2. There is the original 3.4.2b-1026 that does decrypt. But this can only be booted into, definitely not flashed, otherwise you will end up in a bootloop.
I think that from now on, I shall refer back to the 3.4.2b-0623 for decryption. This is identical, but being a different version number, it should avoid confusion.