These are a little different. So these "dual licensed" products work like this:
You get a GPL version of the code, which is free and nobody can charge you for, ever.
If you want to use the software in a way that is not GPL compatible you can opt for the other, paid for, license.
This works in some cases, but in the case of Godot (assuming we were to do something like this) is the MIT license, which already gives you the rights to do whatever you want.
And even in the GPL case, if the other license terms became too odious you could simply switch to the GPL version, and not pay.
You get a GPL version of the code, which is free and nobody can charge you for, ever.
If you want to use the software in a way that is not GPL compatible you can opt for the other, paid for, license.
This works in some cases, but in the case of Godot (assuming we were to do something like this) is the MIT license, which already gives you the rights to do whatever you want.
And even in the GPL case, if the other license terms became too odious you could simply switch to the GPL version, and not pay.