i wish it was that easy. i keep trying to default to esm on node projects but the ecosystem is not there yet, at least in the context of server side nodejs stuff.
That said with "type": "module" in my own package.json files, I've so far never had a problem importing legacy CJS npm packages into ESM, other than the Types are more likely to be wrong (because packages that only publish CJS are more likely to also not publish their own types) or at least inaccurate for the current import approach (returning only "synthetic default" instead of individual exports, for example). That's a bunch of papercuts having to attempt multiple imports until you understand what shape Node is giving you of that CJS import, but after those papercuts I feel like interop is generally smooth sailing in today's Node.
might have to look into it again but there was an issue where some react/jsx/fragment bit had to be ported to esm first.
(My own .tsx based view library doesn't yet have official SSR support, but I do all my testing in ESM in the built-in Node test runner `node --test` so I don't see any complications in doing .tsx on the "server-side", because that is how I'm testing everything already, I just haven't entirely figured out my "hydration" or "islands" or "stamps" approach so I don't officially support SSR yet. It's on the roadmap and I've made small bits of progress towards it, just need to solve it and haven't had the time/priority.)