Linux

Yep, this is a product from Eastern Europe, our public institutions have decades worth of files in Microsoft's formats that we still work with on daily basis and that nobody will ever rewrite from scratch. It's not necessary to support every new feature, but opening stuff from 2000s and 2010s and saving it without compatibility issues is like mandatory if you want to ship an office application here. It's understandable that a company targeting our local markets prioritized OOXML and not ODF. I do hope the Western fork puts more effort into the open format now though.