I'd recommend using ESBuild directly. The following article helped me recently to figure out how to build a browser-side library to publish to NPM, as well as bundling a Node.js server to deploy.

Build A Library With esbuild - How to bundle ESM, IIFE or CommonJS libraries with esbuild

https://medium.com/geekculture/build-a-library-with-esbuild-...

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I had to figure out a trick for Node side to exclude external modules. In my build script:

  const esbuild = require('esbuild')
  const { dependencies, peerDependencies } = require('./package.json')

  const external = [
    ...Object.keys(dependencies),
    ...Object.keys(peerDependencies)
  ]

  await esbuild
    .build({
      entryPoints: ['src/index.ts'],
      outfile: 'lib/index.mjs',
      bundle: true,
      sourcemap: false,
      minify: false,
      splitting: false,
      format: 'esm',
      target: ['esnext'],
      external
    }),