What is the Peer Signing digest on an OpenSSL s_client connection?
Peer Signing Digest is the hash algorithm used by the peer (i.e. the server from the perspective of the client) when signing things during TLS handshake. You will find these places by looking for the term digitally-signed in the TLS RFC.  See for example the details of the ServerKeyExchange message in wireshark:




  .. even with SHA1 hashes disabled on windows


SHA1 is not disabled on Windows in general. It is disabled only for use within the issuers signature of a certificate.