What technology stack to learn to write your own cross-platform applications?

Question

Programming

Knowledge at the moment:
QT level of knowledge beginner-intermediate. I write small projects for my own needs.
What I want to get:
A client-server application that will:
Work on a PC as a separate application
Open as a website page
Have an Android / IOS client (unlikely)
The server should be a database that stores and processes data. Clients only display what they need.
The question is how to make a universal client that would open everywhere with the least labor costs.

Answer 1

As a Javascript option:

• For PC Electron
  
• Service (back end) node.js, express
  
• Front angular, react or vue
  
• For mobile phones react native , ionic
  

Similar for .NET

• For pc WPF client
  
• Service (back end) WEB API (ASP.NET)
  
• Front angular, react or vue
  
• For xamarin mobile phones
  

Answer 2

And what is not satisfied with the same Qt that you already know?

Answer 3

1. Unity/C#
2. NWJS , PhoneGap / HTML, CSS, JS

Answer 4

Flutter for mobile.
Electron as a wrapper for a web application.
Your favorite web application framework.
Your favorite language for backing.

Answer 5

C#
PC - WPF or WinForms
Web - WPF (WebBrowser) or WebForms
Server - ASP.NET or WCF
or Unity client - PC, Web, Android, iOS, etc.