There are strong reasons to be sceptical; there has been no interest in peaceful solutions to Syria’s problems since the violence broke out in 2011.
Hard to see what a trilateral monitoring can do without a UN or similar presence on the ground. What if you monitor a ceasefire violation and can do nothing about it?
That said, this is a new constellation with Russia, Iran and Turkey as guarantors and the RIOTs – Rebels-Insurgency-Opposition-Terrorist – have lost Eastern Aleppo.