It makes no sense 2FA is for like online websites where you don't control the private key but only have indirect access to it, through authentication methods.

In case of a private key, there is no authhentication, the private key is what the money is, and either it's secure or it's not.

In case of like a private key inside a keepass database, one method would be to have both password and keyfile login as well, so that both are needed for accessing the database.

But if the computer is secure, then this is really an overstretch, I'd just go for a password that is easy to memorize.