What limitations exist for encrypted fields?

Encrypted fields in Salesforce indeed have specific limitations, and understanding these can help developers make informed decisions when designing data models.

In this case, encrypted fields are constrained in what they can store, with a character limit enforced by the platform. Specifically, they cannot exceed 175 characters. This limitation arises because longer strings may complicate the encryption process and impact performance.

The other choices represent scenarios that are either permissible or not limited by the encryption feature. For example, encrypted fields can indeed be unique, can have default values, and can serve as external IDs, which allows them to function across various applications without the restriction of length in those contexts. Recognizing these attributes enables developers to effectively strategize how to leverage encrypted fields while being mindful of their character limitations.