how to delete apps on iPad Air 4th gen

See here:

https://support.apple.com/en-us/HT201304

Specifically:

https://support.apple.com/en-us/HT201304#prevent-purchases

In this section on the device, you can allow or disable the deleting of installed apps.

Also not that some apps cannot be deleted by iPadOS as they are system apps/protected and cannot be deleted. See here for those that can be deleted by the user:

https://support.apple.com/en-us/HT208094

You need to check your ScreenTime restrictions:

Settings > Screen Time > Content & Privacy Restrictions > iTunes & App Store Purchases > Deleting Apps - ensure that this permission is set to Allow