You seem to have misunderstood how the sandbox works and what a forced folder is, because they are different things.
A forced folder is simply a folder on your drive that you have marked, from which all programs are launched in the sandbox. This is for convenience and safety (so that you don't accidentally forget to launch something in the sandbox). The contents of this folder are not in the sandbox, and you can do whatever you want with them in the usual way. Except that everything you launch from this folder will be launched in the sandbox.
c:\sandbox\defaultbox is where the sandbox stores files that applications have modified (or created) while running in the sandbox. It does not contain a complete copy of your game/application, only certain files (such as saves). This folder has a specific structure that must be followed for it to work.
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are more details if you are interested. Running applications from this folder will NOT cause them to run in the sandbox. In general, if you do not understand it very well, it is better not to mess with this folder and work with the content inside the sandbox through the Sandboxie Plus interface.
As I already told you, there is no need to move your games and applications anywhere special to run them in the sandbox. You can run any application in the sandbox by simply selecting the appropriate menu item (right-click). The forced folder is only there so that you don't forget to do this.
It is better not to copy anything manually to c:\sandbox\defaultbox.
In addition to Sandboxie Plus itself, you will need to delete the files stored in your sandbox, which is located by default at c:\sandbox. Keep in mind that all changes that programs attempt to make end up in this folder, including your saves. If you decide to uninstall Sandboxie Plus, you must first use Recovery to restore the files you need from the sandbox, and only then delete everything.