XLSX is awkward for scripts, databases and import tools that expect plain text. Parquet is compact, typed and fast to analyse. XLSX is at home in spreadsheets with formulas, formatting and several sheets; PARQUET is the usual choice for large analytical datasets.
One XLSX can produce several PARQUET files; when it does, they are offered together as a ZIP download.
Each column gets one type chosen from all of its values: a column is numeric only if every non-empty cell is a number, and anything mixed, or a value such as a ZIP code with a leading zero, stays text. A workbook with several sheets gives one file per sheet.