.docx (office open xml) is an open published ECMA standard[0], and lots of other apps include support[1], including google which added editing without conversion in 2019[2]

[0]: https://ecma-international.org/publications-and-standards/st... [1]: https://en.wikipedia.org/wiki/Office_Open_XML#Application_su... [2]: https://www.theverge.com/2019/4/10/18304978/google-docs-shee...