Tablet stuck in "Recoery is not SEAndroid enforcing" and cannot turn off Just bought a Samsung Galaxy Tab A6 tablet T-580.

When I buy an Android device I do two things, immediately: 1) get latest OTA update without fully setting the device up (e.g. only Wifi, no Google account), and 2) root, then reformat and reconfigure

I have tried to follow this guide and flashed the linked package with Odin.

Anyway after flashing the device is stuck in the boot logo with the above red error. I can't turn the tablet off.

However I had re-entered Odin mode with a lucky combination of PWR+Home+VDown and re-flashed the binary. However same problem.

Is there anything I can do, including re-flashing a completely stock binary, and try again?
You didn't enable OEM unlocking in developer mode, go to sammobile download your stock firmware (Or do it with smartswitch emergency upgrade and initialization via downloade mode) and reflash stock. 

Then when you are ready to root just enable OEM Unlocking in developer options.