In response to Kamal's 3 questions:
1. As of now (early 2019) Appeon does not have a solution for Linux / OSX end users.
The new C# server-side features support ASP.NET pages. The ASP.NET pages are not automatically generated for you, but PB 2019 does offer a business logic migration solution to "port" your non-visual code and DataWindows/DataStore data objects to C#.
2. Even in the distant future (2021?) Appeon will not provide a solution to deploy / migrate existing Appeon PB applications to the web (os independent cross-browser) without substantial rewrite?
Substantial means different things to different people. There is no magic button you push and most or all the work is done for you. But our business logic migration solution eliminates substantial amount of work compared to rewriting the entire app from scratch.
3. Appeon 2019 does NOT provide a solution to deploy data window applications to the web. It only converts data stores (which are not the same as data windows) to C#. For the front-end UI we will have to write code using some other development tools / environment ?
I the future revision of PB 2019 we plan to add ASP.NET web project type to PowerBuilder Cloud Edition. If you cannot wait for the revision then you can start building out your ASP.NET pages using something free like Visual Studio code and use PB to migrate your business logic to C#.