Overview from independant portal:

Several videos show the presence and involvement of Syrian mercenaries, recruited from the northeast of the country, alongside the Turkish-backed Azeri army. The Turkish and Azeri authorities categorically deny their involvement in these recruitments, despite the testimonies of several Syrian fighters collected by international media.

Full report and source – https://observers.france24.com/fr/20201020-videos-document-presence-mercenaires-syriens-conflit-haut-karabakh