Install shim-signed by entering the following commands in the terminal:
sudo apt update sudo apt install shim-signed
Description:
Secure Boot chain-loading bootloader (Microsoft-signed binary)
This package provides a minimalist boot loader which allows verifying signatures of other UEFI binaries against either the Secure Boot DB/DBX or against a built-in signature database. Its purpose is to allow a small, infrequently-changing binary to be signed by the UEFI CA, while allowing an OS distributor to revision their main bootloader independently of the CA. . This package contains the version of the bootloader binary signed by the Microsoft UEFI CA.
Version: 1.34.9+13-0ubuntu2
Section: utils