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In some scenario, We add custom fields when it satisfy some condition.

In Worker Position Assignments, when Primary Position value is "Yes", Assignment end is "Never", add a description field in Employee form.
STATUS DETAILS
Declined
Ideas Administrator

 Thank you for your suggestion. The functionality that you are requesting would need to be a platform level feature.  This is the same team that provides custom fields, saved views etc.  Please create an idea in the Dynamics 365 Cross Apps - User experience group.