[General Questions and Answers] shadow460:
OK. I had a soft brick due to Android Verified Boot. I have it running the stock unrooted ROM, will try later to root Onn later.

WARNING WARNING WARNING

Some of these tablets are shipping with Android 11

"fastboot --disable-verification --disable-verity flash vbmeta vbmeta.img" does NOT work on these devices. This is a command to disable Android Verified Boot.

YOU WILL SOFT BRICK THE DEVICE if you flash a magisk patched ROM through fastboot without first disabling the Android Verified Boot. It is possible to recover so Read Onn.... (pun intended).

There are certainly other ways to root this tablet and I am all ears to hear them.

END WARNING

I have, in the past, revived devices that appeared to be hard bricked. Most devices these days have an emergency boot block. The Onn 100003562 is no different. During a bootloop, it allows access to the filesystem at certain times. Enter SP flash tools and a known good image of the ROM, including the initial scatter file.

The newest version of SP flash tools is more busted than my tablet was. Get an older one from 2020. Get ADB and fastboot.

Now grab a PC and make a folder in the root directory called ADB. Extract ADB and fastboot into it. The rom image you downloaded should have a scatter file in it, make sure that gets into the ADB directory with everything else.

This is with Windows 10 in mind, but may work on UbuntuMATE 18.04 from my Toughbook, I think the directory there is "home". Get the tablet into fastboot mode (vol up + power), connect it to the PC with a USB cable, then type in

"fastboot flashing unlock"

and press Vol Up on the tablet to confirm. Next

"fastboot reboot" and if it's going to bootloop, it'll do that now.

If you want better control over the tablet, flex it slightly and insert a spudger into the crack that'll form on the side between the device's plastic frame and back bathtub panel. Gently remove the bathtub and locate the jack where the battery connects. Voila, you can stop the bootloop by removing the power!

Get the tablet to start bootlooping. A good way is to either hit the power key or get it into fastboot mode (hold volume up, press power, and hold til the bootloader shows up) then "fastboot reboot".

Unzip the ROM files you downloaded into the ADB folder. Set up SP flash tools and open it (mine requires double clicking the flash.exe file). Click the Format tab and click both "Auto Format Flash" and "format flash except bootloader"

WARNING: do NOT format the bootloader!!!

Wait for the tablet screen to go dark and then hit "start". This will erase everything except what I call the emergency boot block. You should hear the PC ding every few seconds while the tablet is powered up and physically connected to it. The tablet screen will not light up at all for now. Fastboot mode will be inaccessible.

Now on SP Flash Tools, click "Download" and click "choose" on the line with the scatter loading file. Navigate to c:\ADB or Home:\ADB and click the file. If you put the scatter file in another directory, navigate there instead and click it. The scatter-loading file line will populate. Just below it is a checkbox next to "name", uncheck it and ensure ALL the checkboxes are empty in the spreadsheet below that. Check the box next to "boot".

Your PC should still be singing, this means the tablet is bootlooping and searching for a command right after it reconnects electronically to the PC every few seconds. Wait for the USB connected sound then hit "download". The boot.img file will be written to your tablet but it will still continue to bootloop. Fastboot will still be inaccessible.

Go back to SP Flash Tools and check the box next to "name" at the top of the spreadsheet. All the boxes will be checked that you have files for in the ADB directory (or wherever you extracted them with the scatter file). Wait for the USB connected sound, then hit download. Grab a beer or go use the restroom, this will take a few minutes.

When it's done SP Flash Tools will display a message stating such.

Charge the tablet if necessary then press the power key. Bam, no Orange or Red state warning. The white One logo will appear for a few seconds, disappear, and be replaced with the shiny Onn animation. This first boot will take several minutes, so finish up the beer while you wait.

If all is well you should be looking at the inroductory screen. Walk through setup, enable developer options, enable bootloader unlocking, and try whatever it was you were doing again.

I see this forum and our devices as an opportunity to learn. I hope I have been helpful with this, and if I there's something wrong or that can be done better, by all means, post it.

Have a fantastic day!