What happened to the previous (2019) buffer zone that Turkey supposedly had in Syria?

Admittedly I'm confused about the renewed demands of Erdogan for a 30-km buffer zone in Syria.

Erdogan has repeatedly said over the past weeks that he’s planning a major military operation to create a 30-kilometer (19 mile) deep buffer zone inside Syria along Turkey’s border, through a cross-border incursion against U.S.-allied Syrian Kurdish fighters — an attempt that failed in 2019.

I thought they had achieved one such zone in cooperation with the Russians back in 2019? (The one which Erdogan semi-famously waved at the UN.) Or if not, how did that one fall through?