Microsoft publishes their timelines for support. Office 2000 regular support expired in 2004, extended support in 2009. Office 2003 regular support expired in 2009, extended support in 2014. It's reasonable that updates to their recent operating systems won't be tested for such old...
I'm running Windows 11 23H2 and have an installed copy of Office 2007. I opened an old Word document without any problems, although it did say at the header "compatibility mode". I didn't have to take any steps to call up compatibility mode.
Normally I use LibreOffice but I do have a legal...