Same problem here,
Trying to install zorin os 16, downloaded today, via usb on Dell G5 5587 (2019)
"failed to open efi boot..." etc. Same error message as posted before.
With Ubuntu 20.04 the installation worked out of the stick😅
Later, i will try the repair boot options...
Can you please start a thread for you issue to help us keep things sorted and organized? Describe your troubles in detail to help troubleshoot, which Version or Release of Zorin OS and year, make and model of computer.
NOTE:
Dell Inspiron 3847, believe 2015, soon thereafter.
Trying to Install 16 Pro.
Error msg:
Invalid Image
Failed to read header: Unsupported
Failed to load image: Unsupported
start_image() returned Unsupported
Did it for me, thanks a lot