My point is that both Umbra and Cedar mentioned graph support, and I don't believe this was a coincidence.
Umbra highlights: "Groupjoins enable efficient computation of aggregates, worst-case optimal joins handle complex queries on graph structured data, and range joins efficiently evaluate queries with conditions on location or time intervals." while Cedar includes in the hero: "CedarDB is a relational-first database system that delivers best-in-class performance for all your workloads, from transactional to analytical to graph,..."
I think that phrase of "relational first" explains it best. Anything that supports joins can support a graph. Whether it'll perform satisfactorily is going to depend on the compiler and use case/size.
Umbra highlights: "Groupjoins enable efficient computation of aggregates, worst-case optimal joins handle complex queries on graph structured data, and range joins efficiently evaluate queries with conditions on location or time intervals." while Cedar includes in the hero: "CedarDB is a relational-first database system that delivers best-in-class performance for all your workloads, from transactional to analytical to graph,..."