The policy makes the computer distrust recently found to be exploitable bootloader certificates which allow malicious bootloaders signed with those to run through Secure Boot checks. Windows is not in sync with the updates coming from other Linux distros.

Fix: The correct way - you're on a distro like Ubuntu, Fedora or others where you don't even remember having any Secure Boot issues with before: 1. turn off secure boot 2. boot into linux and install the latest software updates, specifically at least GRUB and shim 3. turn on secure boot again