Could not verify credentials... No administrator was found.

Hello!

I'm trying to install Windows on my external SSD following this tutorial: https://youtu.be/3IhW722IMwE but I'm stuck at 12:30 from the video.

Basically, I just installed Windows 10 successfully on the WD Black P50 SSD.

Now, in Recovery Mode, I have to use Startup Security Utility to allow my mac to boot from and external drive.

As soon as I reboot into Recovery Mode, it asks me for iCloud account, then makes me create a new password and after that it says:

"Could not verify credentials because directory server does not support the requested authentication method.".

After closing that window, I click on Startup Security Utility it says:

"No administrator was found.".

I also tried to boot in Single User Mode to create a new admin user. After all the white text, it does not allow me to type the commands and starts Mac OS as usual. I did reset NVRAM/PRAM but still not able to type: the mount -uw | /rm /var/db/.AppleSetupDone | reboot.

BTW, I have macOS Big Sur Beta installed.

Any ideas what could solve this issues?

Thanks a lot!