Our general approach to this is "Show, don't tell".
We feel the ideal way to learn design patterns and SOLID principles isn't to read about them or be told that they're good. It's to make the mistakes yourself and then see how things could be cleaner had you used one of those techniques. Much like code review. You first do things your way, then a reviewer points out how this could be better if you did XYZ instead.
In our product we cover this by offering "Expert Solutions" for each stage. You'll see a code diff (compared to the previous solution), an explanation for that code diff (_why_ were things done this way, what were other alternate approaches), and where possible we even offer a source walkthroughs of the official codebase you're re-creating (the Redis source code, for example).
We have previews of all these features in the demo video: https://codecrafters.io/videos/demo. You can see the solutions in-app without starting a trial, just navigate to the Redis course, click on a stage and then click on "View Solution". And here's an example of a source walkthrough: https://app.codecrafters.io/walkthroughs/redis-event-loop.