Figured it out!
I was logging in with an extension, so mainly just pub key was used with signing done on a per-need basis.
Once I logged in with private testing key, I was able to test Nip-44 DMing.
Would it make sense for Coracle's messaging to request the private key specifically for this purpose? I thought the "Decrypt messages from peers" permission that nos2x-fox asks for would be included, but seems it's not.
Newer versions of nos2x will/do have support for NIP 44, I'm not sure if it's released yet. I don't request the private key because that's poor security practice. So right not it's all a little wonky, but hopefully will be resolved soon.
Nsec.app now supports Nip44, and it works with Coracle, you can try it instead of the extension.