I intend to receive a document stating that I am unfit...

To do this, you need to apply to the Military Medical Commission, that is, pass the VLK.

There is no certificate of unfitness for military service. Its role is performed by the certificate of the military medical commission, which indicates the established diagnosis and the decision of the VLK (that is, fit, temporarily unfit or unfit with exclusion from military registration).

When determining the degree of fitness for military service, the VLK uses the "Schedule of diseases, conditions and physical disabilities that determine the degree of fitness for military service" (appendix to the "Regulations on Military Medical Examination").