Some people say big websites load in 10 seconds, and my website loads in 5 seconds.
Also, when they place the ads; the loading time dramatically increases.
Above the fold means the content that is shown to the users without scrolling down so that they can start reading.
So if your content above the folds load within 3 seconds, and total load time is 15 seconds, then your website is better than the site that loads above the fold content in 6 seconds, and total load time is 10 seconds.
Big websites like Backlinko, and news websites pay more attention to the speed that depends on the above the fold content.
This thing I have explained earlier, but I hope this will make more sense to you.
The above image is taken from the Google site, not from the tool.
You can use GTMATRIX, and see its video how your site is loaded.