https://github.com/guybedford/es-module-shims has a polyfill.

(But it is fairly large: 53KB raw, 15KB gzipped, 32KB minified, 11KB minified+gzipped. It’s providing a lot of likely-unnecessary functionality. I’d prefer a stripped-down and reworked polyfill that can also be lazily-loaded, controlled by a snippet of at most a few hundred bytes that you can drop into the document, only loading the polyfill in the uncommon case that it’s needed—like how five years ago as part of modernising some of the code of Fastmail’s webmail, I had it fetch and execute core-js before loading the rest iff !Object.values (choosing that as a convenient baseline—see https://www.fastmail.com/blog/using-the-modern-web-platform/... for more details), so that the cost to new browsers of supporting old browsers was a single trivial branch, and maybe fifty bytes in added payload. I dislike polyfills slowing down browsers that don’t need them, by adding undue weight or extra requests.)