The top-level package is an ESM codebase, designated by "type": "module" in package.json.
It imports pkg, which contains an export map. One of the "conditions" in the export map is import, which is used when writing import 'pkg'.
You would assume that an import condition in an export map would only point to an ESM module (otherwise, why split behaviour on that condition), however it tries to load the target as a CommonJS module, which results in the dreaded:
/node-subpath-exports/node_modules/pkg/main.esm.js:1
import util from 'util'
^^^^^^
SyntaxError: Cannot use import statement outside a module