I really like the illustrations and explanations. When can we expect the natural transformations chapter?

And also I think there is a small typo at the end of second to last paragraph. "At the same time we have the category of groups, for example, which contains the category of monoids as a subcategory, as all monoids are groups etc.". The roles of monoids and groups are actually reversed - all groups are monoids, but not all monoids are groups.

This style of explanations is awesome. Check out Bartosz Ciechanowski's stuff for a few masterpieces - https://ciechanow.ski/

Very beautiful, have you considered narrating this and putting a play button at the top? x)

Ha, not in this specific way, no. Maybe I will do some videos, though.