Im probably just butting in here, but the “how do i read a directory content” is a pretty standard C# or cpp ask.
Im 100% certain thath either the engine has specific nodes to get the handle and read it to allow you to loop it in BP, or that could very easily create your own custom BP node to do this.
You can actually find thousands of variations of CPP code to just read a file or a directory content.
the gist of it is
get a path, check if file or folder and create a handle for the specific item,
if the handle is a folder you loop over the contents recursively (a recursive function is usually built to do just that) or just the top level files.
With the results that are not . (Same directory) or … (parent directory) you create file handles and usually do what you need to do.
Also, keep in mind the exe’s running in non administrator mode can only read so much - you may want to limit the folder selection to the common locations (documents/saved games/ for windows). The same options for reading do work in cpp for android and IOS but the fail paths become case sensitive.
All of that is obviously very basic File i/o implementation to say the least, I would seriously think UE4 has it’s own similar node to handle all of this…