The Simpsons is available on Disney+ in its original 4:3 aspect ratio for select seasons & episodes. Disney+ will default to the remastered 16:9 ratio for these episodes, but you can switch them to the 4:3 aspect ratio by changing your preferences on the series DETAILS tab.
In order to watch The Simpsons in the 4:3 aspect ratio, use the following steps:
Ensure that the Disney+ app is updated on your device
Navigate to ‘The Simpsons’ series page
Find the toggle labeled “Remastered Aspect Ratio”
Switch toggle to off
NOTE: The Simpsons aired in a 4:3 aspect ratio from its premiere in 1989 to 2010. In 2010 partway through the show’s 20th season, the show switched to a 16:9 format.