So this might be a little offtopic, but maybe not: yesterday I had an illuminating exchange of emails with a person of Free Software Foundation Europe (FSFE) named Lucas Lasota who gave me the advice to report my ISP to the French NRA, "The only action left is to report the ISP's bad behavior to France' telecom regulator ARCEP:
https://en.arcep.fr/forms-services.html " because according to what's written here:
https://fsfe.org/news/2020/news-20200601-01.en.html they adopted a discriminative behavior in my regards, that is they didn't communicate the parameters for connection with alternative hardware. They didn't offer a true alternative to their modem cascading on my apparatus as can be read in the attachment.
Thus when I get the fiber I will try again to ask them for the parameters kindly and if I get the same answer I will report them to the ACERP.
Perhaps it won't change much if only one person does it, but the sea is made of drops of water.
If you want to change your modem and ditch the boxes that come with your subscription for whatever reason you should make your voice heard and this is one correct way.