Watch "Celebrating the 25 th Anniversary of IBM OS/2 Warp - on modern Hardware - 1994-2019" on YouTube
https://youtu.be/NXlrDXLGR_Y
IBM said that they'd open source OS/2 when all parties (read Microsoft) holding key elements of the OS agreed. Even though OS/2 is largely irrelevant today (due to its 32 bit nature), Microsoft still won't let it be open source.
In a fair fight, Windows is dead today, and OS/2 is still being developed. (Probably not FOSS; IBM was no saint.)