Don't know if it is useful, but here you can get latest stock firmware for the Transpeed M98-8K PLUS:
https://drive.google.com/file/d/1TUFhd1Y24rMWS46MacF04fJSosWfKAKR/view
Open Source Version of Allwinner PhoenixCard to Dump, Unpack, Flash Allwinner IMG Files on Linux:
https://github.com/YuzukiTsuru/OpenixCard