This is subset of #48017 as the underlying issue seems different.
I basically have fragment like

    using (X509Store store = new X509Store(StoreName.CertificateAuthority, StoreLocation.CurrentUser))
    {
        // add chain certificate so we can construct chain since there is no way how to pass intermediates directly.
        store.Open(OpenFlags.ReadWrite);
        store.AddRange(clientChain);
        store.Close();
    }
    
    var chain = new X509Chain();
    ....
    bool chainStatus = chain.Build(clientCertificate);

It works on Linux & Windows but it fails consistently on macOS (10.15)
Interestingly, it works if I use StoreName.My instead.

It seems like that store does not have standard OS KeyChain mapping and that is reason why the chain does not build correctly. If that is true, it would be nice if we can feed reference to the keychain or it's collection automaticaly so validation and chain building works consistently across platforms.
In SslStream this primarily impacts cases with client certificates.