French salary, CSG/CRDS and the Foreign Tax Credit
Impôt sur le revenu withheld at source (prélèvement à la source), plus CSG and CRDS social charges, generally exceeds the US tax on the same income. Since 2019 IRS guidance treats CSG/CRDS as creditable, both flow into the same Form 1116 credit.
Your avis d'impôt is the cleanest evidence of French tax actually assessed, year by year — exactly what the credit needs.