At the moment, Windows is unable to decompress the format used by Rack for .vcvplugin (and other things). I was reading the update notes for an Insiders preview, and it looks like Windows will be getting an update that should support the compression used by Rack.
When it arrives in regular Windows updates, it will make a few obscure things just a little bit easier for Windows users/developers.
Ref: Announcing Windows 11 Insider Preview Build 26040 (Canary Channel) | Windows Insider Blog