Hi Tim.
There's no visual ERD-style view of explores, joins, and cardinalities inside Lightdash.
#17241 is the right home for this as it is open and tracks exactly what you're describing.The other issues are older and already closed. Feel free to add your onboarding/stakeholder use case to this issue as a comment. I will also upvote this issue for you so you will be kept in the loop regarding any progress on this.
In the meantime, the closest thing on paper is the
join relationship field (one-to-many, many-to-one, etc.) you can set on each join in your YAML which documents cardinality even without a diagram.