This specific patch is highly recommended for users experiencing application crashes when changing symbology. This issue was caused by a conflict between ArcGIS Pro 2.8/2.9 and certain Microsoft .NET 4.8.x
: Fixes crashes related to changing symbology following certain Microsoft .NET framework updates. arcgis pro 29 patch 5 295 link
You do not need to install Patches 1 through 4 separately; Patch 5 includes them all. This specific patch is highly recommended for users