Merge both wifi and mobile data on Android and IOS

Hi guys,

I would like to find a solution to get both wifi and mobile data.
Please help

How should that work? The device normally switched between the both.

Speedify app can do it. Please check.
But I wonder how do they do it.

That is a VPN app (at least on iOS) - they can do very heavy stuff. Ionic or Cordova is not suited for the tech behind it.