The bug
When playing Minecraft at a small enough resolution that makes the Select Report Category menu unable to be displayed without a scroll bar, the scroll bar that is presented intersects with the outline of the selected category.
How to reproduce
Create a server, and join the server with two accounts
From one account, navigate to the social interactions screen, and select the ⚠️ icon for the other player
Click the Select Report Category button, and select any category option
❌ The option's outline intersects the scroll bar
Can confirm.