I've been trying out different visual settings since upgrading my iMac to macOS Big Sur 11.3, with varying degrees of success.
Big Sur is a lot more opinionated about how it wants things to look compared to previous versions of macOS, and I'm finding that we're not always on the same wavelength.
I can understand why changing the menu bar text and icons from black to white might make sense when used in conjunction with the new 'accent colour' setting which tracks the desktop background colour, but it only works if all the icons follow suit. And the Desktop Quote app, that supplies the text seen in the screenshot above, doesn't.
This has been an issue ever since Dark Mode was introduced, but that is an option I can take or leave, and I've chosen to leave it off. But Big Sur has decided that it thinks its choice is the right one, and the only option I have is to change the desktop background to one that forces the menu bar text and icons back to black.
I have no idea why Apple decided to change this behaviour, other than Because They Can. So for the time being I've opted for a plain green background and green accent.