2021 Release Wave 2 implemented - "Use multiple units of measure when synchronizing items and resources to Dynamics 365 Sales" function. However this function is only useable if unique 1 to 1 relationship exists between Item unit Groups in BC and Unit Groups in D365. D365 for Sales standard functionality sees Unit Groups shared amongst products that are alike. If Business Central is being implemented and you attempt to sync BC Item Unit Groups to D365 you are unsuccessful because you attempt to create a Many (BC) to 1 (D365) relationship.