Plone relations are simply awesome (if you don't know what relations are, please see @pbauer 'Why Relations are awesome" talk). There isn't anything as powerful as relations any other open source frameworks out there. Yet, they are some obstacles in using relations in Plone 6 Volto.
RelationList Widgets are not yet available.
If you have custom content types that use relations, you won't be able to populate them using volto forms as there are no widgets available to handle listing relations and selecting them.
Accessing Relations in Volto
Unlike classic templates you can simply select and display relations in your views. I know there is way to create custom web service but we'll need something that is available as an external addon perhaps.
Am posting this topic to drive some conversation and hopeful find someone who bit more skilled than me to remedy these issues so that relations could simple work out of the box in future releases of Plone.
Thank you @jensens@pbauer. It would be wonderful if you could get this fixed in Buschenschank-Sprint.
I think Relations + Custom content types makes Plone an attractive platform for modern data science projects that need to build new data model by aggregating data.
I have also filed a volto feature request to create necessary missing Relation List and Relation Choice (Not sure if it really work) widgets.
No, so far it only allows getting relations of one item (incoming or outgoing). There you can filter by relationship. Using a second endpoint (@relations-catalog) you can also get all relations of one type.