Cannot install custom version of Spyder 5.5.1

I am unable to install version 5.5.1 of Spyder using Anaconda 3 with “conda install spyder=5.5.1”.
I keep getting “PackagesNotFoundError: The following packages are not available from current channels”
Looking for new channels on has not helped either.

What am I doing wrong, as I’ve installed specific Spyder versions liek this before without a problem.