With registring the device UID in the Apple developer portal and generating a developer certificate/provisioning profile, how long does an iOS/iPadOS app stay working after installed through Testfairy?
Note: i work for TestFairy.
The length of time that makes an app "valid" on device is completely determined by the certificate used to sign the app. It's irrespective of if you install it manually or through TestFairy.
You can sign apps with either a development, adhoc, enterprise or production/distribution certificates. TestFairy doesn't support deploying with production certificates. Developer, Adhoc and enterprise signed apps won't run on your device after the certificate used to sign them has expired. Normally certificates are created with a one year expiration, but say you signed an app 300 days after the certificate's creation, your app will expire after 65 days.