If you are using the IORegistryExplorer on macOS while working with Dark Mode enabled, then you probably noticed the fact that the explorer doesn't fit the new DarkMode, hence the UI might look like that:
I found this article which shows you how to disable DarkMode for a specific application.
Running the following commands:
osascript -e 'id of app "IORegistryExplorer"'
defaults write com.apple.IORegistryExplorer NSRequiresAquaSystemAppearance -bool yes
Solves the issue and make it usable again.