Where is stereo controller

wonderful Dorico 4 but where is stereo controller

If by stereo controller you mean the left/right balance panner, it appears at the top of this image of the Dorico 4 mixer:


The letter C means center. Click and drag on this letter to adjust the left/right balance.

Thanks, John, somewhat dumb of me because it didn’t take immediate effect, all OK now.

However, it does seem reluctant to kick in…