To be honest, any of the apps mentioned will do what you appear to want to do. Garmin's Basecamp is free and is designed to work with Garmin. You can move the route you have planned to the device by simple drag and drop. Any track on your device can be moved into BaseCamp the same way. You can export gpx files from BaseCamp to a folder in your PC. BaseCamp will also convert a track to a route and vice versa. Useful if your planned route has more waypoints than your gpx can contain (max 250 per route for a 32x IIRC)
ViewRanger and its successor OutdoorActive are both free in their basic forms and will let also let you plan a route and export it to a gpx device or import a track from a gpx device. Gpx files can also be exported to a folder in your PC.
The OS app and associated website has similar functionality but requires a subscription as it uses OS mapping, The previous apps can use different map sources such as OSM. It is not as versatile in use but as a planning tool it is as good.
One other tool you can use is GoogleEarth. You can plot a route on the imagery to produce a kml file. Basecamp can read a kml file and will convert it to a gpx file to export it to your gpx device.
Sorry no practical help on Viking but as you see, there are alternatives.
All the above, with the exception of BaseCamp, I believe, require an internet connect as you have to log in to get access to the planning tools but unless you are sitting in a tent planning with a laptop, that should not be an issue.
The final advantage of tools such as the OS app, ViewRanger and OutdoorActive, is they will also run on a mobile phone as navigation apps without a data signal, so they can act as a back up to, or replacement for, your gps.