Can I lock apps in iPad?

Yes, by using the built-in Screen Time.

For built-in apps (Safari, Mail, Camera, etc.), go to Settings > Screen Time > Content and Privacy Restrictions > Allowed Apps, then toggle them on or off.

For other apps, you can set a limit of 1 minute (the lowest it will go), almost effectively disabling the app altogether. Simply go to Settings > Screen Time > App Limits > Add Limit, then select the app and time you want it to be active for.

Hope that helped!