There are no partitioned lookups available in the New UX because there is no logic to filter out the values based on partition because we are not using partitions on the New UX.
Please see the following link:New User Experience: Setting partitions is not available.
Setting partitions is not available. If you use partitions, the default partition that is defined under Account Settings is used when creating project and tasks.
The following lookup values that are defined in Classic Clarity PPM are visible in the New User Experience:
Lookup values that are directly associated with the System partition
Lookup values that are associated with a different partition with the partition association mode set to include ancestors. The include ancestors mode exposes the values to the System partition.