I am working on a project, and would like to make the app grid scrolling horizontal. I'm on GNOME 3.36, and have no idea on how to go about doing this. Can someone help me?
There is no easy, user-configurable way to change this aspect of GNOME Shell. At best, it could be achieved by a GNOME Shell extension, and otherwise, one needs to edit the source code.
In the new version of GNOME Shell, horizontal scrolling of the app grid is implemented. You could thus conveniently inspect the source code of the latest GNOME Shell version to learn how it can be done.