@qGold Quite the opposite, you have the NAM variant which is a dead end.

The NAM variant (U, U1) can't be unlocked in the first place. heroqlte applies to the CN variant (G9300).

Connect to another display and set it back? Sounds like it's just your TV doesn't like it.

US variants can't be unlocked in regular ways. If you insist, see UnSamLock (paid).

Sounds like you don't want to use GNews at all? Why not disable it entirely then?

Interesting that I get to see my creation here. Nevertheless, you should try PHH's AOSP first before any other based on it, and also better luck asking in Telegram instead of here.

That said, a "universal" Android image already kinda exists for modern devices, enabled by Project Treble and in the form of GSIs.

"there are two main reasons why it's not to possible..." - No. The main problem as I see it is proprietary drivers/implementations that aren't available/installable standalone, intentionally so. Work on these is non-trivial and can't be automated.

Few devices support USB video out (requires USB-C 3.0+, neither of your tabs have).

1) TMO Velvet is not BL-unlockable and the linked TWRP doesn't apply, and 2) "backups are broken" refers to TWRP's builtin backup capability.

1) You can boot a recovery and it'll be transient instead of permanent, and 2) strictly using fastboot you can still flash GSIs, but these tend to be more buggy than device-specific ROMs.