If something is still unknown and we want to say that it will happen only in the future that we learn about it, is it correct to say like this:

We already know some details, but the rest is still to be learnt.

If something is still unknown and we want to say that it will happen only in the future that we learn about it, is it correct to say like this:

We already know some details, but the rest is still to be learnt/learned.

EDIT I am not asking what version of past participle of the verb to learn is valid - it would be another question, but instead I mean the structure still to be PP