How is it possible for deaf people to hear individual instruments and pitches from music trough cochlear implants?
Cochlear implant users should not only be able to hear music, but also to enjoy it. To do this, the implant must be able to process a lot of different information at the same time: Rhythm, different volumes, timbres and pitches. Even more enjoyable becomes music according to David Landsberger  if cochlear implant users have binaural input (https://pubmed.ncbi.nlm.nih.gov/31469701/).
Try out what happens if the implant's electrodes do not reach certain areas of the cochlea, for example the tip. Important sound details may be missing and the difference between tones, musical instruments and singing voices can hardly be discerned.
Besides the highly complex technology, it takes one thing above all: a lot of practice, and even more practice. Listening to music is much more challenging than understanding speech. Practice and a sophisticated implant system play together.