Direct umd module import returns different result than aliased import

In Vite/Vue3 app I import two identical umd.js files:
One is in node_modules/foo/bar/dist/foobar.umd.js (and imported with alias @foo = node_modules/@foo).
Second .umd.js file is in <root dir>/foo/bar/dist/foobar.umd.js.

Both paths are resolved, but when imported, the module outside of node_modules is not imported correctly as ES module:

import * as foobar1 from '@foo/bar/dist/foobar.umd' // is in node_modules/foo/bar/dist/foobar.umd.js, works
import * as foobar2 from 'foo/bar/dist/foobar.umd' // NOT recognized as ES module

console.log('foobar', foobar1, foobar2)

foobar1 returns named exports (app, pinia, router), __esModule: true and Symbol(Symbol.toStringTag): "Module"
foobar2 returns only Symbol(Symbol.toStringTag): "Module"

Where is this difference coming from?

If it's relevant, this how the alias (for the correctly imported module) is defined in vite.config.js:

resolve: {
      alias: {
        '@foo': fileURLToPath(
          new URL('./node_modules/@foo', import.meta.url)
        ),
      }
    }

Edit. Vite's dependency optimization seems to be affecting this. If I add to vite.config.js:

optimizeDeps: {
      exclude: ['@foo'],
    },

foobar1 is also not returning named exports, but that doesn't help me much.

Solution

As mentioned in edited question, apparently Vite's optimizeDeps seems to be the key here.
After adding to vite.config.js:

optimizeDeps: {
      include: ['foo/bar'],
    },

this will import named exports correctly:

import * as foobar2 from 'foo/bar' // works! imports named exports
import * as foobar2 from '/foo/bar' // won't work! (even though the path itself is correct)

It is imperative to use the exact same path as provided to optimizeDeps.include.