Hey @PLAY4,
There's no supported way for you to make a mirror material
with Shader Graph. Alternatively, you might consider using a portal and duplicate the geometry to achieve this type of effect.
If you'd like us to consider adding the necessary functionality,
please file an enhancement request using Feedback Assistant. Please include as much information about the experience you're trying to create as you can.
Once you file the request, please post the FB number here.
If you're not familiar with how to file enhancement requests, take a look at
Bug Reporting: How and Why?
Thanks for the question,
Michael