@Erdna Oh - please excuse, but it's easier and with same effect, to pray to Good.
The Display software of bikes are proprietary! I can not imagine, bike manufacturers will be interested to open it for others.
Usually the manufacturer offers a supporting app, to get a connection to the bikes display. But again, each bike manufacturer has its own app.
Sometimes, it would be possible to load a gpx file into the app, which sync it to the bikes display. But mostly only icons and instructions like: "in 50m turn right" will popup on the display. No map, no comfort.
I found it complicated and unhelpful.
Therefore let me suggest: buy a cheap China phone, which isn't a tragedy in case it breakdown after 3 weeks. Better buy a fully featured, robust device, which is developed for use outdoors and on bikes. Then run MyRoute-App on it.