I don't think you're talking about what GP comment is.
For clarification, Bun can act as a package manager like npm (probably the case of "bun + app router + NextJS" comment), and it can act as a replacement to a node runtime a la Express on a VPS (I'm assuming this is what you mean by "yes"). But Bun currently does not implement enough of the Node API's to use Bun as the runtime for a Next.js app.
From Bun themselves: "The Next.js App Router currently relies on Node.js APIs that Bun does not yet implement. The guide below uses Bun to initialize a project and install dependencies, but it uses Node.js to run the dev server."
For clarification, Bun can act as a package manager like npm (probably the case of "bun + app router + NextJS" comment), and it can act as a replacement to a node runtime a la Express on a VPS (I'm assuming this is what you mean by "yes"). But Bun currently does not implement enough of the Node API's to use Bun as the runtime for a Next.js app.
From Bun themselves: "The Next.js App Router currently relies on Node.js APIs that Bun does not yet implement. The guide below uses Bun to initialize a project and install dependencies, but it uses Node.js to run the dev server."
https://bun.sh/guides/ecosystem/nextjs