I'd like to move the camera freely away from player.

The solution i found is to create a dummy entity to set in minecraft.setCameraEntity(myEntity).

So i extended Entity:

public class Cameraman extends Entity {

	public Cameraman(EntityType<Cameraman> p_19870_, Level p_19871_) {
		super(p_19870_, p_19871_);
	}

	@Override
	protected void defineSynchedData() {
		// TODO Auto-generated method stub

	}

	@Override
	protected void readAdditionalSaveData(CompoundTag p_20052_) {
		// TODO Auto-generated method stub

	}

	@Override
	protected void addAdditionalSaveData(CompoundTag p_20139_) {
		// TODO Auto-generated method stub

	}

}

then registered entity type:

	public static final DeferredRegister<EntityType<?>> ENTITY_TYPES = DeferredRegister.create(ForgeRegistries.ENTITY_TYPES, MODID);

	public static final RegistryObject<EntityType<Cameraman>> MY_ENTITY_TYPE = ENTITY_TYPES.register("cameraman", () -> EntityType.Builder.of(Cameraman::new, MobCategory.MISC).build(MODID + ":cameraman"));

	public static Cameraman cameraman;

and finally i try to instantiate my entity:

	// You can use EventBusSubscriber to automatically register all static methods in the class annotated with @SubscribeEvent
	@Mod.EventBusSubscriber(modid = MODID, bus = Mod.EventBusSubscriber.Bus.MOD, value = Dist.CLIENT)
	public static class ClientModEvents {
		@SubscribeEvent
		public static void onClientSetup(FMLClientSetupEvent event) {
			//both not working
			//cameraman = MY_ENTITY_TYPE.get().create(Minecraft.getInstance().level);
			cameraman = new Cameraman(MY_ENTITY_TYPE.get(), Minecraft.getInstance().level);
		}
	}

The result is: Exception message: java.lang.NullPointerException: Registry Object not present: giacomos_prova:cameraman

It seems that i sould register the cameraman entity. How is it done?

You need to register the ENTITY_TYPES deferred register to the mod bus.