I use SharePoint for almost all of my documentation now. It is effectively the intranet for all users and is also set to be everyone’s homepage via Group Policy.
Whilst following a guide on how to add a table of contents to a page, I noticed that I was missing the option under “Content Rollup”.
As it turns out, you need to enable the “SharePoint Server Publishing Infrastructure” site feature to be able to use this:
Once enabled you should then see the option to add a ToC.