My own react app, not using next with a rather heavy payload (async splitting in webpack broke in the past 3 months and haven't been able to get it working again) is under a load of 1.24s Finished time, locally (static content server, with 2 db queries via api).
Unless you MUST have the absolute best SEO, I'm not sure that it really matters having SSR for most people/apps. I don't know how much traffic is really driven from search engines depending on the site, and I really don't know how much you get penalized for having an SPA anymore. I mean if your initial load is under 2-3s and in-site navigation is fast, you'll probably be fine.
The past few sites/apps I've consulted on got the majority of their traffic from outside SEO.
Unless you MUST have the absolute best SEO, I'm not sure that it really matters having SSR for most people/apps. I don't know how much traffic is really driven from search engines depending on the site, and I really don't know how much you get penalized for having an SPA anymore. I mean if your initial load is under 2-3s and in-site navigation is fast, you'll probably be fine.
The past few sites/apps I've consulted on got the majority of their traffic from outside SEO.