Old DTI box

Hi,
normal, yes and no, it depends on what you mean by disconnected.
let's say that what is behind your installation is disconnected from the DTI, yes, it no longer serves a purpose.
However,
the telephone line coming to the DTI must remain connected to it, the technician does not have the right to remove this connection when installing the fiber, it's sabotage, even if it is no longer used at that moment.
You might need an ADSL line with another ISP eventually, later on, but the copper lines will certainly be dismantled starting in 2025.
Otherwise,
it happens quite often that the technician can't get his needle for the fiber through the buried conduit, in that case, it is practical to use the existing copper line as a needle, but in this case, we run the fiber again, plus a replacement copper line for the old one, because there is no reason to destroy what can still work for now.
If that's the case, you have the right to demand the repair of the existing copper line.