There are a couple vertical coordinate systems (VCS-es) you can use with the generic WGS84.
For the ellipsoidal heights, you can use VCS WGS 1984 (WKID::115700). This is native output of GPS if your receiver does not convert your heights automatically. These heights are not very practical for measurements and an analysis might go wrong if you use those heights. For example, river stream might end up going upstream and not downstream. However, a lot of global height data is defined in this VCS.
To measure the height/altitude/elevation you should be using gravity-related VCS-es, which are based on global geoid models (like EGMs) or they are based on some (mean) sea level. EGM2008 Geoid (WKID::3855) is most recent one and ArcGIS Pro has two vertical transformations that allows you to convert between ellipsoidal WGS 1984 and gravity-related EGM2008 Geoid heights. Keep in mind, you need to install ArcGIS Coordinate System Data to be able to transform your heights.
Check also:
List of supported vertical coordinate systems
List of supported vertical transformations