Hi Julie and Xander,
> Is it possible to add a condition within the source for the list ..
Operations Dashboard is not extensible. There are no options to add custom code, nor extend its capabilities. If functionality is missing, please post your enhancement request on the ArcGIS Ideas forum for Ops Dashboard.
> I'm not sure if there is a dashboard for developers edition.
There is no "developer edition" for Operations Dashboard.
> I don't think it is possible yet to use expressions in the list configuration
Correct. The List element does not support the use of Arcade.
> do you have any more information on the outcome of this or is there a roadmap for introducing Arcade expressions in the Dashboard widgets?
Better support for Arcade in Operations Dashboard is planned in a future release, specifically when the app is fully migrated to the ArcGIS API for JavaScript 4.x. (Development is currently working on this.)
> I haven't looked at Arcade too much yet, so I am not familiar with its syntax,
Please take a look at these videos,
Hope this helps,