Yeah I got my preorder a couple of days ago. So far I have not seen a ton of ways to actually write code for this thing using any tool. It is (barely) supported in the Arduino IDE but does not contain any SDK documentation specific to Portenta.
It does look like you can push to either the M4 or the M7 core as they both show up as options. In addition since this board is running mbed, it should work with Mbed Studio but I’m still working on figuring out adapting a generic board profile for it. This seems to be the best short term option as the mbed 6.0 APIs should give access to most of the boards capabilities.