In this leaflet example. When hovered over a cluster marker, it shows the bounding area of the clustered features which is known as convex hull.
Is there a way to reproduce it with OpenLayers?
For anyone who ends up here, there is an OL extension which mimics the same functionality as Leaflet. https://github.com/Viglino/ol-ext
For demo example see: https://viglino.github.io/ol-ext/examples/geom/map.convexhull.html
No, there are no tools yet for this purpose.