Is there a difference? Yes and No.
- learn (v.)
- learned (adj.)
If the word “learn” is used as a verb, then there is no difference at all in the meaning and usage of the words “learned” and “learnt“ in its past form. I honestly don’t know why the spelling is inconsistent. It’s not really true to say that one is US spelling while the other is UK. If you look up a good grammar textbook, you’ll find that both spellings are acceptable. Here are other examples:
On the other hand, “learned“, as an adjective, has a somewhat different meaning, but it’s related to the word “learn“. See this example:
- The Minister is a learned man, so he could speak on a variety of issues.
In the above example, “learned” is pronounced as /learn-id/, which means very knowledgeable.
Whichever spelling you choose, be consistent.