Although strictly speaking that mess is Openreach ‘network’ as it’s between the BT66 ( the grey block on the wall ) and the master sockets in each of the 4 flats ( presumably there are 4 separate cables 1 for each flat ) it’s likely that they were supplied by the developer, and although 3 out of 4 of the flats don’t currently use Openreach based services over those cables , they may in the future, so to start chopping cables may cause future issues , the cable that has the overground repair joint enclosure was presumably provided because someone damaged a cable to one of the flats , hence the repair.
As far as the original question, you do realise that copper and fibre are separate networks, and that fibre networks don’t just replace sections of copper cables with fibre ones, there is much more to it that that.
If these addresses ever have the option of FTTP ‘full fibre’ , as opposed to FTTC ( fibre to the cab ) then those copper cables , the external cable to the BT 66 and the distribution cables to each flat will be redundant and new optical cabling supplied to each flat , as and when FTTP was was ordered
