Thank you Guzzist for your suggestion. I'll check that out if I decide to get a Chromebook.
But I also realized that I didn't need to ask the question. MRA is a cloud app. So I can plan routes on the Chromebook (an assumption I hope is true - can someone verify) and then use my MacMini to accomplish the transfer to my Garmin since I will be doing this before a trip, not while on a trip.