Hey harper, for about 8 years now, I have been happily planning my longer roadtrips on my computer with GoogleMaps. It has offered us up to 10 layers (you can enable/disable viewing in your browser's private session), and when I am satisfied with how I want the route to direct me, I have exported that map as a KML file to a site like
GPS Visualizer - and then had that site convert my KML to a .GPX file.
I have been using OSMAnd+ on my Android phones and a couple GPS-enabled Android tablets (real GPS, not dependent upon cell network access). I simply import that .GPX file into OSMAnd+, and there's my GPS-ready route map. Voice-guided turn by turn, actual route ridden data logging, and many other features are part of it. The OSMAnd app is not tailored only to the motorcycle travel user - which I actually find less limiting. I spend some spare time in my non-riding months (Dec-March) each winter researching all over North America with GoogleMaps & its StreetView to assess & rank roads I aspire to eventually ride in the future. Yes, there is a free version of OSMAnd, but its annual fee for full, ongoing map updates and feature support is pretty cheap on the Playstore.
Here's a link to my current
master_route_planner point archive map I maintain on my own GoogleDrive. I update / curate those points occasionally as I review someone else's Ride Reports - and discover another backroad / awesome secondary highway to add to the pile...
OSMAnd+ always allows you to customize your route on the fly too, and of course you can go create entirely new sub-routes etc if desired.
Though many people like the convenience of direct GoogleMaps navigation on their devices, that option presents limitations quickly (even with their Offlline maps the last few years), so that's why I researched many open-data standard GPS apps and selected OSMAnd+. I often ride in areas with no cell service, so must rely on a genuine GPS receiver-satellite group connection while I navigate twisties on a lonely mountain road.
Hope that offers you another alternative for consideration.