What joystick package are you using? Is it a free one?
I can write some code to help you out. Does the package send Vector2 UnityEvents?
If you can send me an email with further details to email@example.com.
I will be able to help you, and improve the product for others that might this functionality.
I just imported the asset Control Freak 2, and it works like a charm. It coverts the Input System script and allows a joystick to act like WASD, and you can add buttons that act like Mouse0 input. So it got everything working just fine. I probably could have done it without Control Freak had I known that the Inputs were in Input system. I was looking under the player "Mover" script but I didn't find anything there.