Cannot see show deleted messages options

You need to be using iOS 16

The messages must have been deleted....after....you installed iOS 16

The messages must not have been deleted more than than 30 days ago

If there are no messages that meet the qualifications above......Show Recently Deleted will not even appear.

As a test, delete a message that you no longer need. Now check Edit > Show Recently Deleted to see the message.

You need to update your iOS (settings - general - software update) to iOS 16 to see recently deleted