I'm surprised Tesla hasn't made the frunk "soft-close" or auto open/close like the trunk by now...dreams are free i guess.
I don't know if this changed on Firmware 8, but on Firmware 6 and 7, you could do this also if you have an active route, click on the trip tab, and the top would have a volume selector, including mute (which is where I leave my nav since I use Waze).