I would like to get a dynamic stat value on attributes using point cluster symbology, like it is exposed in this topic QGIS 3.10 - Point cluster symbology sum attribute Unfortunately, the answer proposed is not truely satisfactory. In fact making a buffer around each fictive regroupment point does not exactly correspond to the cluster group (even by getting the correct dynamic buffer with @map_scale) because a point can be taken in several buffers while it is affected to one unique cluster group. It can easily be shown with a high density of points.
Since it doesn't look possible directly in QGIS, I've been trying, with a Python plugin, to subclass QgsClusterPointRenderer but the drawGroup method cannot be rewritten, and it is not allowed to subclass its parent QgsPointDistanceRenderer. And I think this is because are maintained in compile C++ to guarantee accelerated rendering, so it's not a good idea to expect to be otherwhise.
As a matter of fact, I think the only way to obtain such possibility would be to have an evolution of QGIS by exposing like @cluster_size and @cluster_color, a new variable @cluster_group as a virtual layer containing all features included in the cluster group, which would permit to make any operation wanted on features directly through the expression variable
If I'm wrong and if a possibility already exists, I would be glad to learn it. On the oher way, is there any chance to see this future functionality integrated on next QGIS distribution?