Looks like that version disappeared recently:
ERROR: Could not find a version that satisfies the requirement mxnet-cu102mkl==1.6.0 (from versions: 1.6.0.post0)
11:39:11
ERROR: No matching distribution found for mxnet-cu102mkl==1.6.0
The top hit from Google for mxnet-cu102mkl
https://pypi.org/project/mxnet-cu102mkl/1.6.0/ is a 404.
There is a 1.6.0.post0
available, apparently added "about 3 hours ago", but I'm a little afraid to switch to it, since such change without a visible explanation smells like an attack attempt.