One thing people don't really think about is that this whole notion of SPA is kind of a pipe-dream, overkill. There might be some apps that are really a single page application (likely just those simple, demo add task apps), but most really can be broken down and composed of many mini-applications.

For example, how often do your users go to their settings page? Does that need to be part of the SPA? Have a complex Settings pages that's composed of 5 or six tabs and 20 different user interactions? Maybe the settings page is itself it's own mini-SPA

How does a user flow through your app, do they really need every screen bundled under a single SPA?

Routing issues, complexity, code dependencies, etc...are all good reasons to not make one monolithic application, even if it's behind a login.

Likely your SPA should really be an app composed of a bunch of smaller SPAs. You search functionality...mini app, your separate workflows...a mini app, your timeline...mini app. history view...mini app, etc...

Breaking your app down into a bunch of smaller SPAs has a lot of advantages and implicit modularization, as well as productivity gains when working on bigger projects with bigger teams.