How to extend display time . I tried brightness and display and cannot change it from 2 minutes

iPad auto-lock will be fixed at two minutes if you have enabled Low Power mode:

Settings > Battery > Low Power Mode

If the problem persists after disabling Low Power Mode, perform a forced-restart of your iPad:

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

Did you try Settings, Display & Brightness - tap on the 2 minutes > on the right of Auto-Lock to reveal the Auto-Lock screen?