Yes, encrypted personal data potentially still is personal data, so some prior thought is necessary. But are you a controller who is processing this personal data? Possibly not. This hinges on what kind of metadata you process, and whether the encryption happens under your authority, e.g. by a software that you provision. If all you can ever get is the encrypted data but not the plaintext, then you can probably treat this similar to pseudonymous or anonymous data.
A related example is a postal service. Letters might contain sensitive personal data. But the postal service is not processing the letter contents, and cannot be treated as a controller of this data. (The postal service is prevented by law from processing this data, you are prevented by the encryption). However, a postal service processes personal data like addresses on the envelope.
You might want to create a Records of Processing document, which will help you understand what (potentially) personal data you will process.
If you are processing patient data on behalf of a healthcare provider, you might want to look into whether you are a controller or a processor. Processor status is not automatic but requires a suitable contract with the controller. As a processor you still have to take appropriate security measures, but you are not responsible for determining the purposes of processing or for responding to data subject requests.