They laid off SDETs circa 2014 (I was one). I don’t think Windows ever had QA people, but it did have automated testing and dedicated people to write and monitor those tests, then file bugs if something broke. But not anymore since 2014.
These days, the only testing any release of Windows gets is from Microsoft employees (Dev/PM) and Windows Insiders.
They have rules of how many hours of self-hosting are required before they can release, but that’s the only requirement. That there exists telemetry of it running.
You might see a gap with that testing methodology, but it might also explain how things like this happen. If it’s a bug that doesn’t prevent boot, it’s easy to ignore.
(I knew a few devs who would just put builds of windows on one of their computers and play a 72 hour long video of a black screen on repeat to get self hosting hours. Then they would proceed with their feature release. And nobody saw any problem with that.)