I am working within classic webmaps and dashboard classic. Will update soon.
What I would like to do, is flash a layer constantly to draw attention to it. In this case in our safety maps I want ships that are being bunkered (fuelled) to flash as long as that activity is valid.
Is this an arcade question?
Thank you in advance,
ideally, the flashing can be done using the points feature, however, since in your case it might vary it will be difficult to play around and set for each of the feature. What you do is create either another layer which stores the center for each polygon along with the attribute activity and use this to set those flashing symbols. Alternatively, you can add a new field and use Arcade expression to calculate the center of the polygon dynamically and use this field for setting the symbol.
please refer to the below link for using arcade expression for center of polygon:
Hope this helps.