Understanding Differences in Area Calculations between SQL Server and QGIS

I have a hard time understanding how a valid area can be returned on spatial data in WGS84 - even the SQL Server documentation confuses me:

Returns the total surface area of a geography instance. Results for STArea() are returned in the square of the unit of measure used by the spatial reference identifier of the geography instance; for example, if the SRID of the instance is 4326, STArea() returns results in square meters.

Any area calculations we make in SQL Server is done on GEOMETRY that is stored in a local projected coordinate system (COLORADO CENTRAL STATE PLANE FEET).

In PostGIS, our data is stored in WGS84, but transformed to State Plane in a query using ST_Transform - which SQL Server does not have the ability to do hence we store our data in projected coordinate system.

I have read that PostGIS Geography will 'pick the best projected coordinate system for the data in the query' ie. it will 'guess' what projected coordinate system to use in order to get valid units.

But - WGS84 is decimal degrees, so back to the main point - is that value you're getting even in M or is it in decimal degrees (even in QGIS?)