I'm not sure about my phone, maybe I'd like to keep Google Lens, but on a TV box it seems completely unnecessary. Its identifier com.google.android.googlequicksearchbox also sounds like it shouldn't contain anything important for the working of a device, but who knows with Google. Is there anything unexpected that would stop working when uninstalling / disabling updates for this?
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.