"Learn" is typically an intransitive verb, but it can also be used transitively. Whether it can be used in the passive voice depends on its usage in a sentence.
Intransitive Usage: When "learn" is used intransitively, it means acquiring knowledge or a skill without a specific object or person causing the learning. In this case, there is no passive voice. For example, "He learned quickly" or "She learned from experience."
Transitive Usage: "Learn" can also be used transitively, with a direct object. In this case, you can construct passive voice sentences. For example, "He learned English" is transitive, and you can create a passive voice sentence from it: "English was learned by him."
So, while "learn" is often used intransitively, it can also be used transitively, and in the transitive form, passive voice constructions are possible.