Can you convert multiple xls or xlsx files to ods without having to do so individually?
You may use document converter.. But why do you need it? It’s true that you should work with native format; but that doesn’t mean you need to convert everything in advance. Keeping documents in their original format and only converting one document when you start editing it, allows you to take advantage from possible import filter improvements in later LO versions that would give you less conversion errors than doing that today.