(I work on Firebase App Hosting, which also supports Next.js directly rather than OpenNext)

I want to +1 that Vercel has been really improving their portability. We still have Next.js specific code in Firebase, and having different architectures can sometimes make us have to figure out the best mapping of their features, but Vercel has made a noted effort to improve encapsulation of Vercel-specific features and portability has improved. I’m honestly surprised that OpenNext, which is not a new project, seems to have gained a lot of attention in the immediate past.