Speculation is rife but missing is any evidence
Ever since Turkish troops began massing around the Kurdish-held Afrin region in the north-western corner of Syria there has been speculation that the anticipated Turkish offensive will take part with a Russian blessing.
Supposedly the Russians are willing to green-light a massive Turkish onslaught on Afrin Kurds in exchange for continued cooperation on winding-down the war and defeating al-Qaeda in its Idlib stronghold.
I think a reminder is in order here that so far we have seen no evidence of this. The one piece of evidence—the report that Russians vacated their base in Afrin—turned out to be completely bogus. The Russians are still in their Kafr Jana base which was established earlier this year precisely to help dissuade Turks from attacking.
For sure the Russians oppose both the full extent of the Kurdish, and the full extent of the Turkish ambition in Syria. As such the fact the two are mortal enemies and can never get along ends up benefiting the Russians somewhat just by default. However, there is no evidence that Russia has ever acted to increase this enmity.
In fact, seeing how the main Russian goal is to prevent Syria from becoming another failed state a massive, destabilizing Turkish-Kurdish conflagration on Syrian territory is in no way in Russian interest.
It is an unavoidable fact that Turkey renewing its invasion of northern Syria and expanding its occupation zone which doubles as a protective umbrella for anti-government Islamists would be a very significant setback for Russia.
Certainly the Russians likewise dislike the prospect of the Kurds carving out a US-backed mini-state out of northern and eastern Syria (an entity which stretching over numerous Arab-populated regions wouldn't even be that "mini"). However the Afrin YPG militias aren't even backed by the US. Their only relationship is shy contact with the Russians.
To have Afrin go from control by isolated and besieged locals with no friends but the Russians,* to control by Islamist-friendly NATO member with an army much larger than Syria's own would be downright disastrous for Russia.
That does not mean that a Turkish offensive is impossible. Just that Russia won't be behind it. Russia is not omnipotent in Syria. If Turkey wants to attack badly enough there isn't necessarily a lot Russia can do without getting into something risky, or hurting its interests elsewhere. Just as it hasn't been able to end continued Turkish and CIA backing for the Islamist rebellion, or Pentagon's attacks on the Syrian army.
*Obviously they also have a friend in the rest of the Kurdish YPG militias, but these can't help except if Damascus allows them passage.