Canon News posted about a patent recently about actively cooling an RF mount camera with an adapter. In this patent, it’s a cooling EF to RF adapter.
In Japan Patent Application 2019-186871 You can see the adapter and the flow of air from the adapter.
Canon News says:
The camera does have to be properly built to handle heat transfer from the sensor to the lens mount, but this is certainly something Canon could accomplish. One of the engineering problems that even Sony and others have is how to cool a sensor that is not fixed in place because of IBIS. Flexible heat transfer materials made of polymer do exist, so it’s possible to cool the sensor directly even with IBIS.
I recently reported that new RF mount adapters were coming, but unfortunately, this wasn’t one I had been told about.