Also check if an Internet connection is active when performing the upgrade. An active connection may be able to help.
In the worst case, however, we can do this:
- Clone the Catalina NVMe SSD to a SATA SSD mounted in an external USB 3 enclosure.
- After the clone is done, connect the USB 3 enclosure to another Hack or Mac.
- Boot the Hack or Mac from its own disk (not from the USB 3 clone).
- Run the Big Sur installer on this Hack or Mac, but when it asks for destination disk, carefully select the external SATA SSD.
- When installation is done and you see the Welcome screen, don't continue, but shutdown the Hack/Mac.
- Now connect the external SSD to the original Hack and boot. At the OpenCore Picker, choose the external SATA SSD.
- Does it boot up?
- If so, mount EFI partition of internal NVMe SSD and EFI partition of external SATA SSD.
- Copy the OpenCore EFI folder from NVMe SSD to SATA SSD.
Keep using the external SATA SSD until you're convinced everything is okay. But
make another clone of the original Catalina SSD and set that clone aside. Make sure the clone has a copy of the EFI Folder in its EFI partition!
Now boot Big Sur from the external SATA SSD and clone it to the internal NVMe SSD. It's good to erase the internal NVMe SSD first. When the clone is done, copy the EFI folder from SATA SSD to internal NVMe SSD.