wp-calypso Legacy Widget: Music Player Doesn't Open Media Library in WP-Admin

Quick summary

In wp-admin, the Choose Songs link doesn't seem to do anything. It should open the media library to allow the user to select audio files or to enter a URL as the audio source.

Here's a video of what currently happens:

https://user-images.githubusercontent.com/3505172/138282342-8fc9953c-06fd-424b-94a1-266972dd4f1e.mov

The issue doesn't seem to be related to a pop-up blocker. It seems like maybe the code that should trigger the modal isn't firing.

Steps to reproduce

Visit /wp-admin/widgets.php on a site with a compatible plan (I tested with Premium and Business.)
Add the legacy widget Music Player to a widget area
Click on the Choose Songs text
Nothing happens

What you expected to happen

I expected to see this modal that allows the user to select audio. This modal appears in the Customizer's widget area, but not in wp-admin:

What actually happened

The modal to select media did not appear.

Context

Customer report #32299451-hc Follow up in 4391393-zen

Operating System

No response

Browser

No response

Simple, Atomic or both?

Simple, Atomic

Theme-specific issue?

No it doesn't seem to be.

Other notes

I've tested on Chrome 95.0.4638.54 and Safari 14.1.2 and it didn't work on either a simple or Atomic site.

Reproducibility

Consistent

Severity

All

Available workarounds?

Yes, easy to implement

Workaround details

The widget works from the Customizer.

Also, the widget produces a shortcode once the music is added. It pulls in the files from the media library by the file IDs.

Example:

[playlist ids="18230,18231"]

This works, but is cumbersome and not ideal for users who need to manage a lot of files. They'll likely have to contact support before they can understand how this works if they don't go to the Customizer first.