dsT = reshape(dataStruct.', [], 1);
DT = datenum([dsT.Year], [dsT.Month], ones(1, numel(dsT)));
MM = [dst.Mean];
ts = timeseries(MM, DT);
However, it is not recommended that you do any further development in timeseries objects. It is recommended that you use timetable objects instead.
dsT = reshape(dataStruct.', [], 1);
DT = datetime([dsT.Year], [dsT.Month], ones(1, numel(dsT)));
MM = [dst.Mean];
TT = timetable(MM(:), 'VariableNames', {'MonthlyMean'}, 'RowTimes', DT(:));
