Is there a way to get headers and sums from 600 workbooks without opening each individually?

I have 600 workbooks with one sheet each and I need to get the headers for each into a single sheet in a new workbook. I also need the sums for two columns and the count of records in each workbook listed on another sheet.

I’ve tried PowerQuery but there are over 69 million lines of data so that crashed. I also tried a few different formulas but none of them have worked so far without me manually typing the entire file path for each file.

I’m in an organization where things are pretty well locked down and I can’t upload things to an online service or download new software. We also don’t have any AI tools for security/confidentiality reasons.

Edit: if it’s relevant I’m using the desktop version of 365 and I’m confortable with formulas and PowerQuery. I’m willing to attempt Macros or VBA but I’m not super comfortable with them.