> I noticed in the past that some Ruby on Rails conference websites were built using React and kinda sucked because they didn't have bookmarkable URLs for when the user clicked on a talk to expand it and read it, preventing users from being able to share direct talk links with others.

You're right that this is a common issue, but it's not inherent to React itself. React apps can absolutely have bookmarkable URLs and proper navigation using client-side routing (React Router, Next.js router, etc.). The problem is that some developers don't implement this correctly, they build everything as modal overlays or state changes without updating the URL. It's definitely a best practice that should be followed, but unfortunately isn't always.