Hello bLuNt_wAcO,
We need more information to investigate further.
Please gather logs from client side (Mac OS X):
https://www.nomachine.com/DT04M00076#6
and on the server side (Windows):
https://www.nomachine.com/DT04M00076#3
Send them to forum[at]nomachine[dot]com making sure to reference the topic in your email.
Did you follow instructions in the article to set up key based authentication with NX protocol?
https://www.nomachine.com/AR02L00785
Especially did you add key properly to the file:
<user's home>/.nx/config/authorized.crt
on Windows server properly.
What’s your NoMachine version on server?
Are you using domain user to login to Windows (in both cases)?