Get familiar with HoloEasy.
HoloEasy is an open-source minecraft hologram library. Under the hood, it uses ProtocolLib for sending packets.
HoloEasy only uses packets instead of registering the entity in the actual Minecraft server.
No, the API wasn't created for only Kotlin users, but rather to provide a clean, fluent API that works well in both Java and Kotlin environments.
For library and plugin devs.