The keyboard shortcuts page (Help -> Keyboard/Mouse Shortcuts) is always black text on a white background.

Since the page is just HTML (%LocalAppData%/Temp/LINQPad6/KeyboardShortcuts.html), supporting dark mode should just require a bit of CSS. I tried the following and it matches LINQPad's dark mode reasonably well, feel free to copy it as-is:

@media (prefers-color-scheme:dark) {
body { background-color: #1E1E1E; color: #DDDDDD; }
em { background: #4C4C00;}
}