There's no "un" highlight for text you type. You have to remove the markup code.

[ highlight ] and such. I put in spaces so you can see it!

If you are having an issue with buttons highlighting or not, that's trickier. I have never had such a problem, but my browser's dark mode sometimes interacts with DU's dark or light mode in ways that make some highlighting odd or nearly invisible.

Hope this helps in some way.