IsSoftDeleted is a provisioning engine virtual attribute, evaluated only at runtime during provisioning operations.

The Expression Builder test tools only evaluate actual user object attributes pulled from Entra (or AD, if hybrid).

Since IsSoftDeleted isn’t stored on the user , it's calculated in the context of:

Whether the user is in scope

Whether the provisioning engine considers them active

The Expression Builder can’t simulate provisioning scope logic, so it can’t test IsSoftDeleted.