What is the ruling on the marriage of a religious man who wishes to limit himself to the Sharia contract (guardian, two witnesses, and imam) and postpone the civil contract in France, on the pretext of its illegality and lack of time, despite the guardian's refusal and his insistence on the necessity of civil registration of the marriage to avoid problems?

The marriage is valid with the permission of the guardian and the presence of two witnesses. Its validity is not conditional upon its documentation in courts. Documenting the marriage is important to secure rights, but marriage should not be delayed for its sake; rather, the marriage should be concluded first, then documented. If your father's intention is to conduct the marriage contract in the civil courts themselves, then it is not permissible to suffice with this instead of the Sharia (definition) contract. However, if his intention is merely documentation, there is no harm in it. You should try to convince your father or wait two months to resolve the disagreement.