LibreOffice fork of OpenOffice (the only fork I ever suggest to anyone) opens and saves in both .odt and OOXML file formats. It's quite flexible. No one is tied to any particular file format unless compatibility with other users is important. Some people
prefer one of the many Rich Text File formats (.rtf). Others would rather share using Portable Document Format (.pdf).
No one has to pay to use OOXML. It is an open standard, plain text, and is not proprietary.
Mac users who use Microsoft Office are not left out of opening .odt files, but it has to be done in
OneDrive rather than the desktop version of Microsoft Office for Mac.
LibreOffice has no problem with OOXML files, so anyone using LibreOffice will find they can open, edit, and save in either .odt or OOXML formats. However, just because LibreOffice can open OOXML files, that doesn't mean LibreOffice has the same feature set
as Microsoft Office.