DUO Mobile is proprietary app that forces one to use their Android/iOS app for 2FA. However DUO mobile's 2FA standard is HOTP counter code (already implimented), and the protocol for importing from their QR code is has been reverse engineered:

https://gitlab.com/kop316/duo-cli/-/blob/master/duo_activate.py

It would be nice if Numberstation could understand and import that code.