[ArcGIS Pro] Setting the symbology for multiple layers in ArcGIS Pro: This is not straightforward, apparently people have done this using scripts (see Stackoverflow). One easy way for a small number of layers is to add a symbology to the “Favourite” galleries and then simply select it for each layer.
Decimate feature numbers using definition queries to speed up display: in ArcGIS Pro, one can set an SQL query to only load every n-th feature using the mod() function and the feature counter. Thanks to Stuart G. for the tip!