In Export > Advanced > Other, add one of the following lines after changing the Codec to dnxhd. vprofile=dnxhr_lb vprofile=dnxhr_sq vprofile=dnxhr_hq
It is possible to get 10-bit by setting the pix_fmt to yuv422p10le or yuv444p10le in Other, but Shotcut is not 10-bit internally. Even if you enable the hidden, unsupported GPU effects, which operates in 16-bit float, it must currently render to 8-bit RGB or YUV before encoding.