Discussions about website architecture become a lot more productive when you use Jason Miller's holotypes idea [1] as your starting point. "Holotypes" is kinda just a fancy word for the common top-level uses of the web. E-commerce, search, media player, etc. With that foundation it becomes obvious that SPAs make a lot of sense for some holotypes and a lot less sense for others. We waste time when we talk as if MPA or SPA is appropriate for all website architectures because neither are and never will be. The uses of the web are just too broad at this point.
[1] https://jasonformat.com/application-holotypes/