Data format error. external table is no tin the expected format for (.xls file format)

Hi there!
Shame that you didnt post Mcode for this query.

Without the code I can just give you this advise:
Power automate: since it is creating the file, surly there must be a way to save it as XLSX.
If this for any reason is not doable:

in power query, you need to change your M code a bit.
This Mcode works with XSLX file right?
This means the query is using to formulas: Excel.Workbook(FileContent( ... ))
However in my expierience with XLS file it actualy needs CSV.Document formula.
So:
1. Open blank work book. 
2. using power query - import this XLS filee using from text/ CSV
3. Copy the formula from formula bar from power Query.
4. Close and Save.
5. go into your file with the error.
6. your current importing formula (probobly called Source -> enter the formula bar.
7. Replace current formula with:
try (Current formula) otherwise NewCopiedformula

Im sorry but without more info / code i cannot do more.