Prologue crashes in multithreaded mode. HappyX is a fullstack framework and has a lot of features and HTTP backends, so your mileage may vary. I can tell you that it will be limited by Nim's async ecosystem, which has many problems. Nexus I don't know.
I would recommend you use Mummy because it's already being used in production and doesn't have async Nim problems. It's also going to be simpler. Stick with React for your frontend and use TypeScript with it. You'll move faster with all the tools available to you. Nim's JS output is massive and slow, and it doesn't have any good tools for debugging. If you're planning on using Next.is, you may as well do that if you're not expecting to have to scale a bunch. Next is a fullstack framework, so it'll handle backend for you if you want. Unfortunately, Nim's web ecosystem is pretty poor, and the only things in it that I recommend in good conscience are Mummy and Gildenstern, both non-async threaded webservers.
