I am experiencing the same with grub-efi-amd64 2.04-1ubuntu26.7.
```
Setting up grub-efi-amd64-signed (1.142.9+2.04-1ubuntu26.7) ...
Trying to migrate /boot/efi into esp config
Installing grub to /boot/efi.
Installing for x86_64-efi platform.
grub-install: warning: Internal error.
grub-install: error: failed to register the EFI boot entry: Operation not permitted.
```
I am experiencing the same with grub-efi-amd64 2.04-1ubuntu26.7.
``` amd64-signed (1.142. 9+2.04- 1ubuntu26. 7) ...
Setting up grub-efi-
Trying to migrate /boot/efi into esp config
Installing grub to /boot/efi.
Installing for x86_64-efi platform.
grub-install: warning: Internal error.
grub-install: error: failed to register the EFI boot entry: Operation not permitted.
```
I also happen to have nvidia-drivers.