You want to sort your Extension Fields, but this is not possible.
SAP Cloud for Customer
Reproducing the Issue
Try to make a custom sort in any Extension Field, but this is not possible.
This is the current system behavior.
Unfortunately, this is currently not supported.
sorting, KUT, extension field , KBA , AP-RC-UIF , C4C UI Framework , How To
SAP Cloud for Customer add-ins all versions