SEO is always hard to get right with SPAs.
I'm running some tests in this direction and to what extent we can leverage Flutter's semantics tree to get good results on SEO. The semantics tree is used for accessibility. It takes some discipline and strategy on the development side to decide what the web app exposes in terms of semantics for each widget. Being a Google technology there are constant improvements in this direction. The interest is that we produce discoverable and relevant results through our apps in their search engine.
Performance is also improved though I have no measured data to provide.
I just observe improvements from update to update on a quite large app which I test upon between dev/master channels. Always on the edge...