I feel like we're at that point around 2010, where Internet Explorer was still dominant, but cracks were appearing. IE was invincible . . . right until it wasn't. If Microsoft doesn't play their cards just right, it won't happen overnight, but the same thing is going to happen. Ten years from now will look unrecognizable.
Windows is in trouble, and they know it. Conservatively the Linux market share has more than doubled globally in just a few years and will likely do it again over the next few. It's not new like Chrome was, but from their point of view, I don't think it matters. It's growth is new, and it's the same.
I would bet virtually anything, behind closed doors, this is exactly how Microsoft execs that have been there for 20+ years are discussing this. They are scared for Windows in a way that has never happened before. And it must be extra dissonant for them, because frankly, Microsoft would be relatively fine even if Windows somehow completely died at this point, but it's also their most important brand, and still a money machine.