the Fast User Switching button was available in the Control Center's "Edit Controls" UI. So there may be a minor bug there.
I've always had Fast User Switching enabled. But after Kevin's description of the changes, I understand your confusion.
I am a developer and encountered this problem in my development workflow while trying to bring my apps to macOS 26, so I had reason to believe it might be relevant for others. Perhaps I'm wrong, but my understanding has always been that this forum is for developers to seek help with any issues they encounter while testing the betas. I've never known that the discussion should be limited strictly to APIs.
Back when Apple last re-launched these forums, they explicitly described them as "meant for code-level questions".
But at the same time, they seem to have removed any limitations on posting so that people no longer have to be members of the developer program. And beta questions still aren't allowed in the Apple Support Community, which is meant for end users. Normally it is an Apple-identified bot (or bot-resembling post) that kindly asks a spammer to spam in the other forums. So therefore, I assumed you weren't a developer.
But in all honestly, even those posts are preferable to the majority of posts in this forum that are simply complaining about Apple's App Review and developer program practices, which I can't do anything about.
So, yeah, I get frustrated with a "discussion forum" full of questions that are impossible for any non-Apple employee to answer.
I've had poor experiences using VMs to go forward in versions. Even installing a beta version in a VM requires a change to the host OS, which then makes your developer system slightly non-standard. I prefer to run betas, and often the current version, on a dedicated test machine. The time I save more than pays for the extra hardware costs.