Is there an app for Only Key on android phone

I’m pretty sure that there is no app for Only Key on Android phone (to enter PIN) and PIN has to be entered using keys on the Only Key device. Just checking in case I missed something.

That is correct, we may in the future allow this through the web app but do not plan on building an Android/iOS app.

I’m not really looking for anything on android phone. I want to use 2FA on Windows laptop.

Sure, there are multiple ways to do that. You could register device as a security key (FIDO2) or use an enterprise solution like Authlite.