Now API doesn't show Flexible effort allocated by assignees. However, you can still use the GET/tasks/{taskId} endpoint with fields=["effortAllocation"] parameter to check total allocated effort.
I used the following query in my test account to get this information: GET/ https://www.wrike.com/api/v4/tasks/IEADG63PKQYWBF4C?fields=["effortAllocation
Could you please extend with the developers somewhere-somehow the mentioned API with this information?
To get back an array instead of just an object which contains the relevant informations (effort allocated by assignees, mode, total effort, percentage).