I've seen a very good article on this: https://www.trek10.com/blog/dynamodb-single-table-relational.... It's an insightful dive into how KV stores can model relational data. However I also feel that these 'NoSQL can do relational modelling!' proponents are kind of hijacking the term: a relational model is understood to be based on relational algebra, and DynamoDB's Everything is One Big Table design ain't it.

NoSQL can model relational data, but it is not a relational model (as understood by E.F. Codd).

Also, NoSQL data access patterns are pretty much set in stone, which is kind of what the relational model explicitly avoids.