I can see the importance of turning off the mileage feature, Waldis.
As of now, this option isn't available in the QuickBooks Online mobile app. I'd recommend sending a feedback request directly to our Product Development team. Doing so helps us improve the features of the program.
Before proceeding, access your account via the mobile browser. Here's how:
Go to the Gear menu and then select Feedback.
Type in your feature request in the description box.