The vulnerability actually isn’t in Windows Boot Manager, it’s a flaw in the image-parsing code of the UEFI itself. That’s why it’s able to bypass SecureBoot.

It just happens that for whatever reason you can easily update the image file from within Windows/Linux itself. The fact they don’t show a logo currently does not mean you’re immune, as the system might just be showing a black screen at that point. Code can be injected into an image file without perceptibly affecting the image output, so you’d likely be able to use a “black screen” logo. If your computer has a UEFI instead of a BIOS, which is pretty much everything from the last 10yrs, then you are more than likely at risk.

My computer likely isn’t susceptible, and that’s because it’s a Dell workstation. While the bug still exists in the image parser, Dell has locked things down so it’s pretty much impossible to change the boot logo from userspace.