As of now, it doesn't actually do anything, but a hidden setting that controls back gesture sensitivity has surfaced in Android 11. The new "Gesture Settings" screen (accessible via a hidden activity) has a pair of sliders that may eventually control how the edge back gesture added in Android 10 works. At least you can enjoy a snazzy animation in the meantime.

The new options live in a hidden activity in the Settings app on Android 11 (com.android.settings.Settings$GestureNavigationSettingsActivity). You can easily access it via any app that allows you to search for and launch application activities, like Activity Launcher, just by searching for "Gesture Settings."

Gesture Settings, in all its glory.

Again, unfortunately these sliders in the hidden Gesture Settings don't actually work. Whether you set them to the minimum or maximum sensitivity, behavior right now remains unchanged, but we do see an animation on the sides of the screen that shows an area for... something related to the back gesture expanding and contracting as you change it.

Presumably, when it does work, these sliders will control something about how the back edge gesture works — and a tweak really is necessary. When Google implemented the new navigation system, sliding navigation menus were affected. Although the company added a tap-and-hold-the-edge "peek" gesture, using any case with a lip near the edge of the screen makes it impossible to trigger. I assume that this new back sensitivity setting will control how far inward you have to swipe to trigger the back gesture, (potentially expanding the area you can use to trigger the "peek," as well, but we can't be sure).