Having a table of contents is essential to make the post navigation easier and that’s the reason for using a table of contents. Please note that if you don’t want to use a table of contents you can safely ignore that test, as is true with any other, you don’t need to follow the guidelines entirely and should instead give priority to your SEO strategy.
Those guidelines are just in place to help guide people that are not so familiar with SEO. Plus, you can also disable any of the tests from running on your page by applying the following filter with the test name: https://rankmath.com/kb/filters-hooks-api-developer/
Some may think that it’s a usability factor. Makes the navigation easier. Not SEO factor. And it is usually used on blogs and not all websites have blogs. you could replace with something more meaningful. But a good UX usually leads to better rankings. If a visitor lands on your website and sees just a block of 2000 word text – they might bounce back to SERPs to find something more “digestible”.
With that said, we agree it is not for every website and that is why we recommend not paying too much attention to the score. it is supposed to be used as a to-do list and you can easily ignore the items that do not apply to you.