I cannot edit my last post, so sorry for double posting. But I wanted to share the solution.
Since list_users_storage_objects_async does not work as intended retrieving other user’s data, I searched more and found this post here in the forums. My best guess about why it does not work here is about the cursor, but I have absolutely no idea how to populate the cursor on the client side.
So well, the solution was use @zyro’s RPC code, and now it works, successfully implemented. Now that it works, I will implement @yamlcoder’s ideas for a better more efficient code. Thank you all!