If there is anything to worry about, Secure Boot is the issue people should be worried about

As long as the firmware on your computer supports setting up your own keys or those you trust, there is no problem.

The issue is: most people don't know this or check this, so there is a potential systemic problem with Microsoft having the root keys.

At the moment PC users seem to be safe, Microsoft hasn't caused problems (intentional or otherwise).

When fwupd installs updates of the firmware on your machine (or dual boot and install Windows updates), that could change, in theory.

Very likely the option to disable Secure Boot will also remain (as I understand it, that is what these companies say they will do), so there is that.

So it's very much theoretical, but also shows the Linux world is not in complete control.