In the early seasons of Star Trek: Discovery, ships in Starfleet use an interesting technology that rarely appears elsewhere in Star Trek. In the twenty-third century, when ships in Starfleet need to communicate with each other or with the Federation, they do so using holographic communicators. Throughout seasons 1 and 2 of Discovery, transparent semi-colored holograms flash into existence on the bridges of various starships – even Klingon vessels communicate with colorless holograms in Discovery. Nevertheless, after the USS Discovery jumps forward to the thirty-second century, the holographic communicators never appear again on Discovery.

https://screenrant.com/star-trek-captain-pike-power-change-discovery-holograms-op-ed/