Fully working Big Sur on external SSD - booting fails on cloned internal SSD

I have successfully created a fully working Big Sur config on an external SSD.

After cloning the the external SSD to an internal SSD on my Hackintosh (using Big Sur Disk Utility in Recovery Mode on my Hackintosh), and copying the external SSD's EFI folder to the EFI folder on the internal SSD booting fails:

Black screen, Apple logo. Progress bar keeps empty . . .

Any suggestions?