In the past Assad has negotiated with them.
He did not in Afrin.
He told them to surrender to the IRGC and the Quds forces, disarm and take allegamce to him. They refused the offer and Assad/Putin told Turkey to “go for it”
That lead to the fall of Afrin.
It was funny.
The Kurds allied with NATO to oppose Syrian government, but whinge about Assad not preventing Turkey (a member of NATO) from attacking them.