Finally got TWRP working. Had to source info on a TWRP.img from forum.xda-developers.com - because also booting into the atvX firmware's recovery would not initiate. Very frustrating
Link is to a different firmware ROM for the purpose of installing TWRP, that ROM installs thru TWRP, so a functioning TWRP is mandatory. Source Link:
https://forum.xda-developers.com/androi ... m-t3751720
That forum link's main post has two embedded Mega download links to "Custom" universal Amlogic s912 TWRP.img :: either 2gb-ram-twrp.img OR a 3gb-ram-twrp.img ~depending on how much ram your device has.
Easy FIX:
1) Install Official TWRP App from a Google Play store thru mirror or fork.
- Used apkmirror.com
2) Download the twrp.img file (14mb) from above forum.xda-developers.com link that matches your devices ram, Save in device internal storage at partition > /sdcard/
3) Open Official TWRP app
4) Select TWRP FLASH
5) Select Device > Android Emulator = twrp (don't download thru twrp)
6) Select file to flash > twrp.img from your storage /sdcard/
7) Select > Flash to Recovery
-Device should flash, then in app settings Select Reboot in Recovery, and should start in TWRP recovery. If done correctly you will have installed TWRP v3.2.1.0
Hope this helps those looking to reinstall TWRP.
This Fix should work for all s912 devices running the atvX-firmware version v2FF or older.
Edit: the new Official TWRP.apk v1.21 doesn't let you pick file from internal storage when you link TWRP to your Google account, or allow image from external SDcard to Flash the TWRP-Recovery. So use v1.19 or older.
Second Edit:
Here I found this link to a TWRP tutorial that has TWRP downloads for the Amlogic S905, S905X, S912, and the new S905x2 ....
Link:
https://androidpctv.com/tutorial-instal ... x-amlogic/