I create a distribution cert in developer.apple.com, and I downloaded it, and double clicked it in the download folder on the mac. The cert appears in Keychain Access, but it does not seem to have a key associated with it.
In Visual Studio (Windows), 16.5, in tools > options > Apple Accounts, it says that the certicicate is "Not in Keychain".
Any help in how to resolve this?
From shared screenshot , that's no problem about Development Certificates ,you will see the private key after clicking the down arrow .And it shows Valid in VS from PC(THINKPAD2).
However , the Distribution Certificates can not seet the down arrow . You should be sure that this Certificate is created from a new CSR file Mac to generate the Distribution Certificates .You can not use other people generated CSR file or Development generated CSR file to generate a Distribution Certificates .
By the way , if certificates is in System Group , you can copy it to Login Group . Then it will show private keys .
