Keep TNT with fiber

If the existing cables, which the technician has no reason to touch, remain, the TNT stays with it.

I personally demanded when the technician came that the fiber goes from the electrical panel to my box in another room through the walls, not on top.

He informed me that during construction, the holes in the walls were undersized and made on the cheap (copper cables and antenna together) so there was no more space, and he asked for permission, which I granted, to remove the copper since there will never be ADSL again.

The technician is not authorized to destroy or disconnect anything without your permission, or unless, in a condominium, a general assembly has approved the replacement of all the wiring in the common areas, but then at the expense of the designated company, not your technician.

I don't know.

It all depends on whether Numéricable also provides TNT via its coaxial cable or if the coaxial cables (at least from the other rooms) are or aren't connected to the rooftop antenna (and also whether the future installation won't be full fiber but FTTH that would use the existing coaxial cables, but I don't think so; there wouldn't be a need for internal installation).

If TNT is currently only provided by Numericable, you’re out of luck; it will be up to you to reconnect the cables to the rooftop antenna (and it's not guaranteed that you won't need to ask the syndic for permission).

The fiber box can indeed communicate with the box via Wi-Fi, but this is never a good idea; the Wi-Fi speed will always be lower and can be unpredictable. It's always better to run a network cable (possibly inside the walls), as the installation is supposed to ensure that the box is placed in the room of your choice.

Rushing the installation of the fiber box in a congested electrical cupboard often leads to unpleasant surprises, interference, or other issues; this is what happened at my kids' place, and it doesn't work unless the cupboard door is kept open, not great...

You will inevitably step back to jump better since, in the medium term, everyone will be forced to install fiber with the disappearance of the copper network; the operator cables are not really, but I suppose their survival will also be limited.

The problem is less the cable than what goes through it: once you subscribe to a fiber plan, the Numericable one will be canceled; the fiber installer, the cable connections, he doesn’t care: he will use the same holes or others, leaving the installation in place, it’s not his problem.
You can always ask Numericable if it continues to transmit the TNT alone for non-subscribers via the rooftop antenna, but I believe even less a word of it since it should continue to go through a box that we will no longer have.

Back when my mother was around, her building was wired for Numericable, which she eventually canceled to switch to an ADSL subscription, everything remained in place.

If I remember correctly, the Numericable outlets had 2 outputs, one for the cable, one for the TNT antenna (it remains to be seen if it was connected to the roof or not, but it seems to me that it was, because, very geek for her age, she had a DVD recorder that wouldn’t have been able to function as a dual tuner without an independent antenna).

In a collective building, the cable doesn’t date back to the Antichrist; I find it surprising that there wasn’t an antenna before, even if unused.

Otherwise, this incurs connection costs (or antenna installation if it’s an individual house).
The alternatives are a multiple TV subscription, the Molotov solution or equivalent (also theoretically paid starting from a TV) is shaky since it involves recent and "smart" TVs, which may not be the case in the bedrooms, and it also raises the issue of bandwidth sharing if the WiFi is used to watch 3 or 4 movies at the same time.

You will anyway step back to jump better since, in the medium term, everyone will be forced to install fiber with the disappearance of the copper network; the operator cables are not really, but I suppose their survival will also be limited.

The problem is less the cable than what goes through it: once you have subscribed to a fiber plan, the Numericable one will be canceled; the fiber installer, the cable connections, he doesn't care: he will go through the same holes or others while leaving the installation in place, that's not his problem.
You can always ask Numericable if they continue to transmit TNT only off the rooftop antenna for non-subscribers, but I believe even less of it since it should continue to go through a box that we won't have anymore.

Back when my mother was in this world, her building was wired for Numéricable, which she eventually got rid of to take an ADSL subscription, everything remained in place.

As far as I remember, the Numericable output boxes had 2 outputs, one for the cable and one for the TNT antenna (still to determine if it was connected to the roof or not, but it seems to me that it was since, very geek for her age, she had a DVD recorder that could not have worked with a dual tuner if there wasn't an independent antenna).

In collective buildings, the cable is not from the antichrist, it seems surprising that there wasn't an antenna before, even if unused.

Otherwise, it leads to connection costs (or antenna installation if it's an individual house).
The alternatives are a multiple TV subscription, the Molotov solution or equivalent (also in principle paid starting from a TV) is shaky since it involves recent and "smart" TVs, it may not be the case in the bedrooms, it also poses the problem of bandwidth sharing if the Wifi is used to watch 3 or 4 movies at the same time.