>> Avalonia's big money-maker is their drop-in replacement platform for WPF, which allows you to basically take an old WPF application and turn it into a Windows/macOS/Linux/web application with two lines of code, if you're willing to pay the price

Forgive my ignorance. But what "price" you are talking about, money, or dev time spent to root out the kinks?

I have a WPF application running on Windows, and I am thinking about porting it to Avalonia for the purpose of cross platform. Just for the background