YB1-X90F Not Booting into OS - Flashing Help [Android]

TL;DR: Noob needs to stock flash a device that won't boot into OS. How is that possible if guides steps tell you to enable the "Developer options" and "OEM unlocking” on a working phone?

Fault: Powers on, shows the orange Lenovo splash screen, then it’s just blank. I can access the bootloader and recovery.

I’ve asked this over at XDA and a subreddit with surprisingly with no response. There was also another person with what seemed to be the same issue, no reply.

I acquired this and a Huawei MediaPad M5 8.4 SHT-W09 with the same type of issue. Not booting into OS. The M5 was really easy. Just added a file(s) to an SD card and run it from the recovery menu.

Doesn’t seem to be that simple with this though. But I am a noob.

I took me ages to get a working driver for ADB. Seems to be working now. (Mentioned in the XDA link.)