@mohd-akram and I incorrectly deduced that duplicate named exports resulted in those exports being excluded.

However, this is not always the case!

With the following code:
a.mjs

export function foo() { return 'a' }

b.mjs

export function foo() { return 'b' }

dupe.mjs

// the order here doesn't matter!
export * from './a.mjs'
export { foo } from './b.mjs'

test.mjs

import { foo } from './dupe.mjs'
console.log('out:', foo())

> node test.mjs
out: b

dupe.mjs should export foo from b.mjs. This is because explicitly named exports DO override export * exports.