Warning: Some posts on this platform may contain adult material intended for mature audiences only. Viewer discretion is advised. By clicking ‘Continue’, you confirm that you are 18 years or older and consent to viewing explicit content.
If you have already made a certificate and imported it with mokutil maybe you just need to select the MokManager.efi from your screenshot and start that to enroll the key.
https://www.dannyvanheumen.nl/post/secure-boot-linux-shim-mokmanager/ seems to be a good introduction to the concept. Your distribution should have specific documentation on how to make custom kernels and secure boot work if you need more details.
If you have already made a certificate and imported it with mokutil maybe you just need to select the MokManager.efi from your screenshot and start that to enroll the key.