managed to mount something with the correct size but it's all empty, nothing on it.
Just to be sure, you are aware, that Workbench is not a file explorer, aren't you? It only shows icons (.info files). An MS-DOS disk usually does not contain any Amiga icons.
To see all files you have to use the DOS shell/CLI or a file manager. Only in AmigaOS version 2 or later there is a menu item Window -> Show -> All files which you can activate.