A monthly folder often holds several useful extracts and a few files that don't belong in the report. Select the intended files before combining them. A temporary workbook can look like a valid extract but contain draft rows. Keep a source-name column when someone will need to trace a result back to its file.
In native Power Query, the folder connector lists files, and Combine Files creates helper queries from a sample transformation. The local editor combines the supplied practice files with the same per-file header principle. It doesn't scan your computer or create a live folder connection. Promote each file's header before stacking its rows; promoting only the first row of the combined output leaves later headers among the data. Different row counts on the hidden files test whether your combine remains repeatable.