As a consequence of Brexit, when you order products to be sent from a supplier in Great Britain (or indeed any other country outside the EU) for delivery to France, you become liable for French TVA and customs duty, depending on the value and nature of the product.
So it is quite possible that instead of receiving your parcel as before, you will receive from the post office or the transport company a demand for payment of TVA and customs duty, plus a fee for presentation to the customs authorities (la Douane Française), with a warning that no delivery can be made until you have paid. Although customs duty is not theoretically due on shipments worthless than 150 euros, TVA is due from the first euro and the fee for presentation to the customs authorities is likely to be payable in most cases.
How can one avoid these extra charges?
There is more information (in French) on ordering goods on the internet from non-EU countries from the Douane Française website here https://www.douane.gouv.fr/fiche/nos-conseils-avant-dacheter-sur-internet and a useful flow chart (in French) here [Achats-en-ligne-Dois-je-payer-des-frais-supplementaires-a-la-livraison-de-mon-colis.pdf] or by clicking on "Download 1" below.
As a further warning, a number of spammers and hackers try to make out that you have tax and duty to pay on a shipment on its way to you. These will be sent by text or email. Please ignore any of these as genuine transporters will contact you by letter or, for La Poste, your postman may call at your door to explain there are delivery charges to be paid.