Not sure why Amazon has not listed a specific f/w for 12th Gen HD8 Plus.
The bin file from the .de site is the same as on the .us one. However, I copied it into the root of "internal storage" and thought If I hit "check for updates" in the "About" section it would find it... but it didnt. So I took the risk, did a factory reset and searched for OTA Updates . the 126.96.36.199 was available (not the .4) so I installed that. Now everything works fine for now with the Google Play Store. Difference was that b/c I connected to wifi, I registered the Fire tablet right before doing anything else.
Thanks for the help!