The category set in Default Post Category is not selected in the display when posting a new post.

Description

The category set in Default Post Category is not selected in the display when posting a new post.

Step-by-step reproduction instructions

1. Go to Writing Settings in Settings
2. Select any category in Default Post Category
3. Add New Post

Expected behaviour

The category you checked in Default Post Category is checked when you submit a new post.

Actual behaviour

The category set in Default Post Category is not selected in the display when posting a new post. Once you draft, save, etc., it will be checked.

Screenshots or screen recording (optional)

Code snippet (optional)

WordPress information

• WordPress version: 5.7.2
• Gutenberg version: Not installed
• Are all plugins except Gutenberg deactivated? Yes
• Are you using a default theme (e.g. Twenty Twenty-One)? Yes

Device information

• Device: Desktop
• Operating system: Mac OS X 11.4
• Browser: Chrome 91.0.4472.77