It doesn’t sound right to me that simply having the navigation turned on would preclude listening to the radio as well. The navigation will certainly cut across the radio when it needs to deliver the next direction, but beyond that it should just work away in the background. If that’s not the case, I’d say you have a problem within the system.
My insiders at Honda tell me that the MY2021 HR-V (released last month) has an upgraded entertainment system that has been developed in response to customer input and is said to be a better all-round device with greater connectivity. At this stage, there’s no word on whether the system will be able to be retro-fitted to your model Honda, but there’s a chance that it might be. A chat with your dealer sounds in order.