It is definitely not solved for the vast majority of SPAs out there. Where it is solved, it is not solved for free or cheaply, as it would've been if these apps used server-rendering tech.
In practice, what happens is Google spends their JS rendering resources on the top sites and will very rarely render a new site. Generally, assuming you stay clear of all the gotchas, Googlebot can eventually "see" your JS-rendered content but it will certainly take a lot longer to be indexed and, therefore, it will take longer to appear in search results. If you or your clients rely on organic search traffic for your site, then picking client rendering based tech is certainly a bad decision.
[1] https://developers.google.com/search/docs/advanced/javascrip...