How to add x-scheme-handler in GTK application?

Question

Adding MimeType=x-scheme-handler/xyz; to data/package.desktop.in isn't helping.

Answer 1

It seems that the app has to be installed for the x-scheme-handler to be detected, merely running it from GNOME Builder won't help.

Steps for installation:

1. Click on the Build from the omnibar, followed by Export Bundle in the same dropdown.

2. Open a terminal in the directory that opened after the export was done.

3. Run flatpak install yourapp.flatpak

Thanks to developers in Matrix chatroom for helping out.