Forget convertion i was in a similar position years ago and i did something easier faster and i think smarter.
just make a winform with nice big controls take care of docking scaling anchors etc so that it will look nice and can be used with small smart devices.
Make sure you pass some start program parameters in your app and when a special parameter is passed instead of opening the main typically desktop form of your app open that new one in fullscreen.
Now the tricky parts isnelsewhere. I hade setup a tiny windows 2008 r2 server that allows remote apps to be run on it.
Create a user account that you will allow access to that server and only that app of yours with the specific parameter we talked about. (Ex myapp.exe -remote)
The what ever device he will get you can download the free app like 2x rdp or microsoft rdp in android. Make a new connection to your server (you can use any free ddns you like if you dont have a static ip) and connect with that windows server account you did before.
This account if has been properly setuped will only run your app and will only show that new mini winform you did..
The end user will do a simle click and from his internet connection will do a simple remote desktop that is linited to your app only. (Router configuration is needed once)
That way you will keep maintain just one source code and he will have low bandwidth cost and can continue his work without data loose in case of disconnection.
I use that for years in mobiles tablets and pos systems. Its fast its stable its secure its easy to maintain (nothing on the client side) and you don't waste months of learning wpf or doing xamarin converting.