This Seeking Tech guide will explain how you can disable the heads-up display in Gran Turismo 7.
You can use the following video as a visual aide:
Step 1: First off, make sure you go to the final screen before you start a race.
Step 2: Next, select Settings.
Step 3: You then need to select Display Settings.
Step 4: Finally, set Race Info Display to Off.
This can also be done during the middle of the race in the Settings menu of the pause screen.