I searched a little, but didn't find much specifically about using an OBD2 Bluetooth Scanner on the 2018. I've never had one at all.
In general, people seem to recommend this:
With the Torque app.
I did see that there is an app called "ActiveOBD for Subaru", but I don't see much info after 2017.
Before I purchase a device, I wanted to be sure I'm getting the best setup for the 2018.