Auto-lock greyed out and cannot be enable (low battery mode is off)

As you may be aware, 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:

• On an iPad with a Home button: Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

• On an iPad with Face ID: Press and quickly release the volume up button, press and quickly release the volume down button, then press and hold the top button. When the Apple logo appears, release the button.

You might also check that Date & Time and TimeZone are also correctly set for your iPad - as these settings are known to cause various functional issues if incorrectly configured:

Settings > General > Date & Time

If these settings are similarly greyed-out, you have a ScreenTime Passcode set - which must be temporarily removed before some settings can be changed:

Settings > ScreenTime > Change ScreenTime Passcode > Turn Off ScreenTime Passcode

Having myself acknowledged that you may be aware that Low Power mode can inhibit access to some settings, additional information was provided of other settings that may be a source of the issue.

If you have digested all of the suggestions made - it may be necessary to reset your iPad settings. While this reset will not cause any loss of data, as a precaution, it is always wise to ensure that you have a current iCloud or iTunes backup before performing the reset:

How to back up your iPhone, iPad, and iPod touch - Apple Support

When you are happy to proceed, you can perform the reset from iPad settings:

Settings > General > Transfer or Reset iPad > Reset > Reset All Settings

If the problem still doesn’t clear, the next step is to reset the iPad to factory settings:

Restore your iPhone, iPad, or iPod to factory settings - Apple Support

Otherwise, you would be best advised to seek assistance directly from Apple Support. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively and perhaps easier, you can initiate and manage your support cases using the excellent Apple Support App. If not already installed on your iPad, the App can be downloaded from the App Store:

https://apps.apple.com/app/apple-support/id1130498044

You might also visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to test and assess your iPad - and you can explore your available options:

Genius Bar Reservation and Apple Support Options - Apple