Does Silverlight for macOS support 64 bit? Does Silverlight for macOS support 64 bit?
If so, from what version?

If not, when will it?
Development of Silverlight ended back in 2013 except for security and bugfixes. It's been dropped from the major browsers starting in 2015 and will be discontinued entirely by Microsoft in 2021.

So the answer to your first question is "no".