CondaValueError: Malformed version string '~': invalid character(s)

This looks like it was fixed with Conda 4.6.0. Upgrading your Conda should resolve the issue.

conda upgrade -n base conda

If you have trouble solving environment, I suggest trying

conda upgrade -n base -c defaults --override-channels conda

This will exclude all other channels during the solving process, and helps because having too many options to prune is one of the main reasons for slow solves.