Windows11 Prompts "Secure Boot KEK Update" Should I Install It?

Yup, You should but you have until June if you would prefer to read up on it first.  I've been working on it for all our work computers to make sure we get there by June.  Also, it won't break anything to not do it yet, it will just impact security update stuff after June. I read they are adding to make it visible somewhere now because the certs that are being updated are used before login and it was a pain to get their details a few month back.

https://support.microsoft.com/en-us/topic/secure-boot-certificate-update-status-in-the-windows-security-app-5ce39986-7dd2-4852-8c21-ef30dd04f046