Best way to provide external clients access to specific Kanban boards only?

[Dani Lynch]

I have a business need to have our DataCenter Jira instance accessible by only internal team members (for regulatory purposes), but a small subset of the data needs to be shared with external clients - primarily from Kanban boards. 

I’ve proposed Issue Security schemes of internal/external but there seems to be less of an appetite for this as our users will not reliably set the flag accurately and it would not reference board type. (There’s also still the regulatory piece of external vs internal user accessibility to Jira)

Some options being explored are: use of Miro, Trello or a separate Cloud instance where the external users are able to be provisioned and the needed issues are synced from Jira. Miro seems to be a solid solution, but there are different challenges here since we rely heavily on Elements Connect fields for Jira workflow validations

Looking for feedback to from the community on how folks have accomplished this sort of work sharing mechanism outside of orgs. Do others face this challenge of balancing regulatory access constraints with client agreements on visibility of work?