\startuniqueMPgraphic{square}
draw roundedsquare(20,20,2) withrgbcolor (.625,0,0);
\stopuniqueMPgraphic

\defineoverlay[square][\uniqueMPgraphic{square}]

\definedescription
   [task]
   [text=\uniqueMPgraphic{square}, width=broad]

\setupitemgroup
    [itemize]
    [1]
    [symbol=square]

\starttext

\section {First try to change symbol}
\startitemize[1,columns]
\dorecurse{10}{\item itempoint \par}
\stopitemize

\section {Next try to define an own description}

\startcolumns
\dorecurse{5}{\task very long sentence i will now write to create this weird issue \par}
\stopcolumns

\stoptext