The bug

When a message containing a special character (such as a line feed) is displayed within the Select Chat Messages to Report screen, its special characters are displayed without applying any special formatting.

How to reproduce

1. Open a world to LAN
2. Run the command:

   /tellraw @a {"text":"Hello\nthere!"}

3. Spawn a creeper
4. Run the command:

   /execute as @e[type=creeper,limit=1] run say hi!

5. Open the Social Interactions menu
6. Start a report for the creeper (MC-253497), and select the "Select Chat Messages to Report" button

Result

Instead of

Hello
there!

(or alternatively, Hello there!) being displayed in the list of messages, the control character for a line feed is displayed.