Ask HN: How do you test performance of navigations between pages?

I’ve been reading up on how to measure and analyze website performance. Every tool and article I’ve come across is focused on performance of single page loads. However, my understanding of various SSR frameworks is that loading a website for the first time can be very different from navigating to another page on the website. For example, Next.js’s page router will only request the JSON of an SSRed route when navigating. That can change the perceived experience for the end user. Why is there so little focus on testing page navigation speed? (articles and tooling) Am I looking in the wrong places or has SEO made information like this impossible to find? Any suggestions on articles or tools to look at?