By CMAF ULL, I assume you are referring to the LL-HLS or the LL-DASH protocol standards that use partial fragments in the CMAF container format.
We are currently working on partial fragment support in AMS. That has been ongoing work for us this year, and we hope to have a release out before the end of the calendar year. Currently we are in testing and stabilization phase with multiple players.
At this time, for reduced latency in AMS, see the options here.
https://learn.microsoft.com/en-us/azure/media-services/latest/live-event-latency-reference
We will be updating our Release Notes and informing in the portal when the LL-HLS feature is ready to use.