1. The “location” key was replaced with the “alternative” key.
2. You need the “counter” key to share counters.
\setupenumeration[alternative=serried,width=broad,distance=0.5em]
\defineenumeration[theorem][text=Satz,title=yes]
\defineenumeration[corollary][counter=theorem,text=Korollar]
\starttext
\starttheorem[title={Pythagoras Theorem}]
The square on the hypotenuse is equal to the sum of the squares on the other two sides.
\stoptheorem
\startcorollary
The sum of angles of a quadrilateral is 360 degrees.
\stopcorollary
\stoptext
Wolfgang