We have added a new attribute to the cost plan object. This attribute needs to be secured in the modern UX. We have added a rest API Key and I can see it in the grid views.
The attribute does not appear under the administration \ attributes screen though
Attributes from the Financials object are FLS enabled (fin_financials table).
Attributes from the Cost Plan (fin_plans table) and Cost Plan Details (fin_cost_plan_details table) are not.
There is a feature on the pipeline to enable FLS on both the Cost Plan and Cost Plan Details object, but this is still undecided on when is going to be implemented.