5 years for a “permanent” WA card (a special Brexit concession as it’s 2 years for other similar cards, and 6 months for 5 year card holders. Passports are scanned, so stamping doesn’t matter at all.
Anyway it is up to each EU State to decide, and stamping of residents’ passports is not contrary to EU law or more specifically to the WA (which doesn’t provide for any exemption). So there is really no argument to make.
“depending on national practices and in accordance with their legislation, some Member States may still stamp passports of beneficiaries of the Withdrawal Agreement, even if these hold a notified residence documents. Please note in this regard that the … Commission guidance is legally not binding upon the Member States. Therefore, Member States, which stamp the passports of beneficiaries of the Withdrawal Agreement do not necessarily act in breach of Union law.”
The only TCN residents exempt from stamping in France under EU law are family members of an EU citizen with the appropriate permit under Article 10 of Directive 2004/38.
No, it is perfectly allowable, see above!