The attached dyn takes a chosen directory and looks for all of the .xlsx files within it and returns their file paths. At this stage, you could sort by filename if desired. If you have variable worksheet names (unlike just using Sheet1 or a similar default) you can query the worksheet names using the Bumblebee package.
The Data.ImportExcel then brings in all of the data from the Excel files. Set showExcel to false to stop it visually opening every file. Depending on how many files, and how large they are, it might take some time. Once it is complete you will have a 3D list where @L3 are the workbooks, @L2 are the rows, and @L1 are the column values. You can then do whatever data manipulation you want. In this simple example, it merely flattens the top level so that the resulting 2D list can be written easily to one worksheet.
The final step is then to write it out to a single workbook.
Hope this helps,
Input and Output Excel