While trying to figure out how to get Quick Look working in Catalina (still working on that one). I found some great tips on installing plugins for additional features here sindresorhus/quick-look-plugins.
Here's the 3 simple steps for getting code to render and check out the above repo for more.
brew is suggested to install the plugins and is required for this guide.
Step 1: Install the plugin(s). There are many more if you poke around.
brew cask install qlcolorcode
Additional removal of quarantine attributes steps for Catalina
Step 2: List the attributes you will be removing with
xattr -r ~/Library/QuickLook
Step 3: Remove the attributes
xattr -d -r com.apple.quarantine ~/Library/QuickLook