Lenovo Yoga Tab 3 Pro (YT3-X90L) factory image, OTA update or backup needed

i was playing around trying out some new stuff with my yoga tab and locked it.

I’ve tried to factory reset it, but it’s still locked. I’ve tried to flash twrp in hope to do something more, but to unlock my tab in locked state isn’t allowed.

There is an old Google Account on it, but i can’t remember it and now i’m sitting in front of my tab and staring on it and thinking about how to help my self. I can’t, i need your help 🙁

thank you in advance for any help i can get

UPDATE:

I’ve tried so much things now. 1.) https://www.youtube.com/watch?v=nCzrnnh2K1w I was able to follow this tutorial to minute 9:08. But the option “Email and password” is not there anymore. I guess they patched it with 6.0.1. 2.) I tried to flash a stock rom or twrp with LenovoDownloader(QcomDLoader). The stock rom file is: Lenovo_Yoga_Tablet_3_YT3-X90L_ENG_S200028_1609230146. even its a german device this file was the only one i could find. But the LenovoDownloader won’t recognize my device. The windows stays white, no entries. I guess i installed the correct driver for this device and Windows recognizes them as removable device if i plug it in via usb. 3.) i’ve tried to use adb and fastboot boot oem unlock. But this commands aren’t working in locked state. 4.) With a trick i could open the Settings and was full of hope to active the developer options to set usb debbuging to active. But this developer options aren’t available either with this “user”. 6.) there is an apk for showing the “Email and password” interface. I could install it, but it force closes right after starting it. 7.)I’ve tried several tools to bypass this FRP: WinDroid Toolkit, D-G Unlocker, Realterm, but NOTHING.

What could i do further? I’m out of ideas right now

Specs for the device: Lenovo Yoga Tab 3 Pro YT3-X90L Lenovo/YT3_l0_row_lte 6.0.1/MMB29M/LenovoYT3-X90L_S200307_170614