arcpy.management.ApplySymbologyFromLayer(ref_to_your_layer, path/to/your/symbology/layer.lyrx, None)

in_layer = YOUR CODE TO CREATE in_layer
in_symbology_layer = YOUR CODE TO CREATE in_symbology_layer

aprx = arcpy.mp.ArcGISProject("CURRENT")

aprxMap = aprx.activeMap # NOTE(!): 'aprx.activeMap' is only supported from Pro 2.1 onwards!!! activeMap returns None if script is called outside a running application according to ArcGIS Pro Help.

aprxMap.addLayer(in_layer, "AUTO_ARRANGE")
in_layer = aprxMap.listLayers(in_layer.name)[0]

aprxMap.addLayer(in_symbology_layer, "AUTO_ARRANGE")
in_symbology_layer = aprxMap.listLayers(in_symbology_layer.name)[0]

in_layer = arcpy.ApplySymbologyFromLayer_management(in_layer,in_symbology_layer,update_symbology="MAINTAIN")[0]