To add a code block, type @ and scroll down to "Code Block <>". It's still very limited, with syntax highlighting limited to C/C++, Java, JavaSript, Python.
When I type @ there's no code block option. I get People, Smart Chips, and then in "Building Blocks" I get five items from "Meeting Notes" to "Project Assets". If I click the arrow to expand to the full list of building blocks, it only adds a sixth item "Launch Content Tracker" and the rest is blank space.
Which is too bad, it's the one thing keeping me from writing design docs in google docs.
Funny that they paywalled that feature, while tools like Colab are free.
Generally, Google has made code-related and academia-related tools freely available. Oh well.