Gdevelop 3d falling

I’m working on a 3D open-world action-adventure game and wanted to make it so that the player will fall when he is not on the ground. I am using a 3D physics extension but don’t know how to determine the condition of falling. For the record, I wanted the physics to be just like Grand Theft Auto 4’s Euphoria system. Here is a photo of what it looks like, and below it, there’s a link to a funny GTA 4 Euphoria Physics.
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Please, I would appreciate the help and support to keep GWD going strong!

Thanks!