Raspberry PI4 8gb error after update => grub rescue

Hello I already installed 3x freedombox on a Raspberry Pi 4 Model B 8gb according to the instructions with the EUFI firmware on a sdcard and freedombox on an bootable ssd via usb connection.
At the first boot everything works (rainbow screen) freedombox is running. I will update freedombox to the latest version.
The update is successful.
Then I do a reboot.
After reboot I get an error:
symbol ‘grub_is_lockdown’ not found
grub rescue>

I did some research but to no avail
grubrescue> ls (gives me some output)
… (hd0,gpt2)…
grubrescue> ls (hd0,gpt2)/ (gives me all the files/maps like /boot …)

i saw solutions at grub> but not at grub rescue

what happens here ?