The first "Guide" column also needs to be made consistent in verbiage because some entries are noun phrases ("TLS configuration") and some indicate activity ("Verifying"). WDYT about:

TLS configuration
Resource loading
HTTP redirection
HSTS implementation
Clickjacking prevention
CSRF prevention
Secure cookie configuration
MIME type verification
CSP implementation
CORS configuration
Referrer policy enforcement
robots.txt configuration
SRI implementation

Sounds reasonable. I've mostly used these, with a couple of tweaks. I also tried updating them on the page titles too, for consistency.

This does mean that way more titles now break onto two lines in the sidebar and pages themselves.

Do you think that is a problem?

To be checked later after updated preview links are available

My preference is to use only the acronym in the sidebar (short-title) and the expanded title on the page, so:

title: Cross-Origin Resource Sharing (CORS) configuration
short-title: CORS configuration

One of the things this can help with is that when you're on the landing page, you can quickly match up the guides from the table's first column to those in the sidebar. At the moment, you need to parse the titles in the sidebar a bit.

With both the expanded form and acronym in the page title, the page will still be searchable in the "Quick Search" field using either the long form or acronym.

But I'll leave it to you to make the call. The glossary pages have acronyms in the sidebar - I don't know if we have a strict guideline or any guideline around this.