GOST R 34.12-2015 is technical standard belonging to the russian GOST R standards. The hash described in this document is called Kuznyechik. It is a variant of the GOST R 34.11-94 which produces a 256-bit hash.
This variant uses the parameters present in RFC 7801 https://datatracker.ietf.org/doc/rfc7801/.
This online tool allows you to use the GOST R 34.12-2015 (Kuznyechik) Hash.