I mean… DX 9, 10, and 11 were all released prior to Nadella being CEO/chairman.

But in software, it’s very commonplace for library versions not to be backwards compatible. This isn’t the same thing as being able to open a word doc last saved on a floppy disk in 1997 on Word 365 2024 version, this is about loading executable code. Even core libraries in Linux (like OpenSSL and Nurses) respect this same schema, and more strongly than MS.

Using OpenSSL as an example, RHEL 7 provides an interface to OpenSSL 1.0. But 1.1 is not available in the core OS, you’d have to install it separately. 1.1 was introduced to the core in RHEL 8, with a compatibility library on a separate package to support 1.0 packages that hadn’t been recompiled against 1.1 yet. In RHEL 9, the same was true of OpenSSL 3 - a compatibility library for 1.1, and 1.0 support fully dropped from core. So no matter which version you use, you still have to install the right library package. That library package will then also have to work on your version of libc - which is often reasonably wide, but it has it limits just the same.