if the user is storing the data in our app but the data is not encrypted then do I need to encrypt data even if we do not fall in GDPR?
This reply assumes that you are doing some of the processing and/or storage, as opposed to leaving it all on the user's device.
The GDPR does not directly mandate encryption. Article 32(2) says:
In assessing the appropriate level of security account shall be taken in particular of the risks that are presented by processing, in particular from accidental or unlawful destruction, loss, alteration, unauthorised disclosure of, or access to personal data transmitted, stored or otherwise processed.
So you need to think about how sensitive the data is likely to be. Then design your data processing and management practices (e.g. which employees have access, what procedures must they follow) accordingly.
So the upshot of all this is, no you don't have to encrypt the user's files, but doing so might well be a good idea.