RemoveSystem.cs

using Unity.Collections;
using Unity.Entities;
using Unity.Jobs;
using Unity.Mathematics;
using Unity.Transforms;
using UnityEngine;

public class RemoveSystem : JobComponentSystem
{
    [Inject] EndFrameBarrier barrier;

    protected override JobHandle OnUpdate(JobHandle inputDeps) => new Hitcheck()
    {
        mousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition + Vector3.forward * 10),
        commandBuffer = barrier.CreateCommandBuffer().ToConcurrent()
    }.Schedule(this, inputDeps);

    [Unity.Burst.BurstCompile]
    struct Hitcheck : IJobProcessComponentDataWithEntity<Position, ItemTag>
    {
        public EntityCommandBuffer.Concurrent commandBuffer;
        public float3 mousePosition;
        public void Execute(Entity entity, int index, ref Position pos, [ReadOnly] ref ItemTag data1)
        {
            if( math.distance(pos.Value, mousePosition ) < 1)
            {
                commandBuffer.DestroyEntity(index, entity);
            }
        }
    }
}

public struct ItemTag : IComponentData { }

Spawner.cs

using Unity.Entities;
using Unity.Mathematics;
using Unity.Rendering;
using Unity.Transforms;
using UnityEngine;

public class Spawner : MonoBehaviour
{
    [SerializeField] MeshInstanceRenderer rendererParams;

    void Start()
    {
        int maxCount = 6400;
        var random = new Unity.Mathematics.Random();
        random.InitState();

        float3 min = new float3(-10f, -10f, 0), max = new float3(10f, 10f, 0);
        var entityManager = World.Active.GetOrCreateManager<EntityManager>();
        var archytype = entityManager.CreateArchetype(
            typeof(MeshInstanceRenderer), 
            typeof(Position), 
            typeof(ItemTag));

        for (int i = 0; i < maxCount; i++)
        {
            var e = entityManager.CreateEntity(archytype);
            var pos = new Position() { Value = random.NextFloat3(min, max) };
            entityManager.SetSharedComponentData(e, rendererParams);
            entityManager.SetComponentData(e, pos);
        }
    }
}