There have been several discussions about slow package operations on Windows 10. I have a similar problem on MacOS (Big Sur, but also the previous version; Julia 1.5.3).
I observe that anti-virus uses a lot of cpu during Pkg operations (Sophos). I excluded .julia from scanning.
It has been suggested that Pkg unpacks the registry in a temporary folder before copying to .julia. Perhaps that is the reason. Does anyone know that temporary folder’s location so I can exclude it from virus scanning?