Several light switches are non-functional, all lamps are working

At our place, a lamp outlet was covered with a box because the previous tenants (and we too) do not need a 3rd lamp at this spot. Do you have something like that as well?

I am rather assuming 5-core lamp cables, in which at the moment only one “channel” is switched. But this needs to be checked to know for sure, at the moment everything is just speculation.

The 2nd picture is an additional wall/ceiling outlet, right?
That's exactly what it will be for.