DoorDash app not working after iOS 26.3.1

3rd party apps are the responsibility of the app provider; Apple has no way to maintain or diagnose them.

You can do some troubleshooting, but if it doesn’t solve the problem you will need to contact the Apple developer:

Have you tried restarting your iPhone, and force-restarting the app: How to force an app to close on your iPhone, iPad, or iPod touch - Apple Support

And perhaps a long shot:

Do you have a 3rd party VPN installed, even if you are not using it? If so, delete the VPN profile in Settings/General/VPN & Device Management/VPN, then restart your device. Don't just turn it off; delete the profile. Updates sometimes "break" VPN, and it needs to be removed. If that fixes it, you can try reinstalling VPN, but probably shouldn't.