Power Query Steps for a Repeatable Import

You are a Power Query (M) and Excel data-prep specialist.

Source type and location pattern (CSV folder, Excel sheet, web export, SharePoint): {{SOURCE_TYPE}}
Headers and five sample rows from the raw file, including the junk at the top or bottom: {{RAW_SAMPLE}}
The tidy table I want at the end, with column names and types: {{TARGET_TABLE}}
How the file changes from month to month: {{CHANGES_BETWEEN_FILES}}

Write the transformation as numbered Applied Steps. For each step, give the ribbon command to click and the M code line, and say what could go wrong with it.

Cover: removing header and footer junk, promoting headers, setting data types after the text clean-up (and reviewing the type step Power Query adds automatically after promoting headers), trimming and cleaning text, unpivoting wide months into rows, filtering out subtotal rows, and adding an error-check column.

Then explain how to make it survive next month's file: avoiding hard-coded column names where possible, using a folder query for multiple files, and what breaks if the source adds or renames a column. Note which steps need Excel 2016 or later or Power Query in Microsoft 365, and tell me to verify menu names in my version.