Post Content Block hangs when you try to add it to a page

[kjellr]

Describe the bug

When I try to add the "Post Content" block to a page, the browser tab becomes unresponsive.

To reproduce
Steps to reproduce the behavior:

1. Activate the Full Site Editing experiment.
2. Create a new page
3. Try to add the "Post Content" block to your page.
4. Note that the page freezes/errors.

Screenshots

After clicking to insert the Post Content block above, the page freezes, or produces the error here:

Editor version (please complete the following information):

• WordPress v5.4.2
• Gutenberg v8.4.0

[kjellr]

Ah, sorry — this is a duplicate of #22080.