Systems Design is a formidable topic because it can go in so many directions. This is a good guide. Might I also recommend something that includes caching, partitioning, indexing, and NoSQL vs SQL. More detail can be found here https://www.educative.io/courses/grokking-the-system-design-...
I remember using the course you have linked to some time ago - it was very useful. I noticed now that the course is sold on a subscription model. I don't remember being that the case. Would you happen to know when that changed?
