Event Storming is a method to elaborate a domain model together with domain experts and technologists in a sticky notes session. The resulting diagrams are gradually refined further and can be structured in such way that makes the suitable to do code generation of the boilerplate code that is needed to implement the domain.
One great tool to use is Miro, but this is a proprietary and commercial SaaS platform. There do no exist any good FOSS tools that are a replacement for the intuitive features that Miro offers. Another SaaS platfrom that supports collaborative sticky note whiteboarding is Mural.
There is a great open source tool in the making for collaborative UX design. It is called Penpot. It has a whiteboarding kit, that comes close to the functionality that is needed. So I created a feature request on their community forum (and send a toot about it too):