Depending on how up to date a person's device is some folks can only see some unicode sets. Unsupported emoji characters are rendered as blocks. In the edit view, let's make sure to replace emoji with visual image placeholders like we do in the published view. See also #29831 (comment)

Steps to reproduce

1. Starting at URL: https://wordpress.com/block-editor/post or /wp-admin/post.php
2. Visit a site such as https://getemoji.com (one recommended here)
3. Copy and paste a less common but still frequently used emoji (basically pretty much anything other than a smiley face)
4. Enter it an a post

What I expected

The classic editors displays the emoji itself.

Starting at https://wordpress.org/gutenberg and following the same steps, the emoji will appear.

What happened instead

Though very low priority (it's fine in the post), it'd be nice if emojis would appear as the emoji itself instead of a square box. Found this when writing my own posts.