qtwebengine h264 broken on Windows

I could be doing something wrong here, but at a minimum I think more documentation clarifying this would help a lot of people. From what I can see searching on Google, I'm not alone at having to figure all this out.

Qt's 6.2 and 6.5 documentation for WebEngine states that "proprietary codecs" (including listing h264) can be enabled in WebEngine by adding the configure flag "-webengine-proprietary-codecs"

When you do this and WebEngine is properly configured (QtWebEngineCore isn't disabled for a myriad of other reasons), the configure summary confirms that proprietary codecs are enabled. Furthermore, the Gn flags passed to chromium include use_proprietary_codecs. However, the chromium build produced will not include support for them.

Since 2018, Chromium requires the use of clang to enable h264 support. See also this forum post referencing the problem. Using MSVC silently disables h264 in Chromium.

However, QtWebEngine doesn't seem to support building without MSVC. When you try to set platform to "win32-g++" configure gives you this warning: "WARNING: QtWebEngine won't be built. Build requires Visual Studio 2019 or higher."

So far as I can tell, it's not possible to use h264 with QtWebEngine in its current state. Please correct the documentation or let me know if I am missing something.