Sample concept of using OnPickup inplace of Interact in order to detect the used hand.

1_PickupAsInteract.cs

using UdonSharp;
using UnityEngine;
using VRC.SDKBase;
using VRC.Udon;

[RequireComponent(typeof(VRC_Pickup))]
public class PickupAsInteract : UdonSharpBehaviour
{
    [Tooltip("Receives events: OnInteractLeft, OnInteractRight")]
    public UdonBehaviour eventTarget;
    private VRC_Pickup pickup;
    private Vector3 pos;
    private Quaternion rot;


    void Start() {
        pickup = (VRC_Pickup)gameObject.GetComponent(typeof(VRC_Pickup));
        // cache original transform data
        pos = transform.position;
        rot = transform.rotation;
    }

    void OnPickup() {
        // get the hand state, false = right hand
        bool leftHand = pickup.currentHand == VRC_Pickup.PickupHand.Left;
        // force drop the target
        pickup.Drop();
        // may not be needed, but I like the guarentee of enforcing the original transform after bring dropped
        transform.SetPositionAndRotation(pos, rot);
        // trigger event
        eventTarget.SendCustomEvent(leftHand ? "OnInteractLeft" : "OnInteractRight");
    }
}

2_PickupAsInteract.asm

.data_start

    .export eventTarget
    
    instance_0: %UnityEngineGameObject, this
    type_0: %SystemType, null
    Type_0: %SystemType, null
    instance_1: %UnityEngineTransform, this
    instance_3: %UnityEngineTransform, this
    instance_2: %UnityEngineGameObject, this
    GameObject_0: %UnityEngineGameObject, this
    objA_0: %SystemObject, null
    objB_0: %SystemObject, null
    instance_4: %SystemObject, null
    instance_5: %VRCSDK3ComponentsVRCPickup, null
    Int32_0: %SystemInt32, null
    instance_6: %VRCSDK3ComponentsVRCPickup, null
    instance_7: %UnityEngineTransform, this
    position_0: %UnityEngineVector3, null
    rotation_0: %UnityEngineQuaternion, null
    instance_8: %UnityEngineGameObject, this
    GameObject_1: %UnityEngineGameObject, this
    Boolean_0: %SystemBoolean, null
    instance_9: %VRCUdonUdonBehaviour, this
    eventName_0: %SystemString, null
    instance_A: %VRCUdonUdonBehaviour, this
    eventName_1: %SystemString, null
    pickup: %VRCSDK3ComponentsVRCPickup, null
    pos: %UnityEngineVector3, null
    rot: %UnityEngineQuaternion, null
    eventTarget: %VRCUdonUdonBehaviour, this
    leftHand: %SystemBoolean, null

.data_end

.code_start

    .export _start
    
    _start:
    
        PUSH, GameObject_0
        PUSH, instance_0
        COPY
        PUSH, Type_0
        PUSH, type_0
        COPY
        PUSH, instance_0
        PUSH, type_0
        PUSH, pickup
        EXTERN, "UnityEngineGameObject.__GetComponent__SystemType__UnityEngineComponent"
        PUSH, GameObject_0
        PUSH, instance_2
        COPY
        PUSH, instance_2
        PUSH, instance_1
        EXTERN, "UnityEngineGameObject.__get_transform__UnityEngineTransform"
        PUSH, instance_1
        PUSH, pos
        EXTERN, "UnityEngineTransform.__get_position__UnityEngineVector3"
        PUSH, pos
        PUSH, pos
        COPY
        PUSH, GameObject_0
        PUSH, instance_2
        COPY
        PUSH, instance_1
        PUSH, instance_3
        COPY
        PUSH, instance_1
        PUSH, rot
        EXTERN, "UnityEngineTransform.__get_rotation__UnityEngineQuaternion"
        PUSH, rot
        PUSH, rot
        COPY
        JUMP, 0xFFFFFFFC
    
    .export _onPickup
    
    _onPickup:
    
        PUSH, pickup
        PUSH, instance_5
        COPY
        PUSH, instance_5
        PUSH, instance_4
        EXTERN, "VRCSDK3ComponentsVRCPickup.__get_currentHand__VRCSDKBaseVRC_PickupPickupHand"
        PUSH, instance_4
        PUSH, objA_0
        EXTERN, "SystemObject.__GetHashCode__SystemInt32"
        PUSH, Int32_0
        PUSH, objB_0
        COPY
        PUSH, objA_0
        PUSH, objB_0
        PUSH, leftHand
        EXTERN, "SystemObject.__Equals__SystemObject_SystemObject__SystemBoolean"
        PUSH, leftHand
        PUSH, leftHand
        COPY
        PUSH, pickup
        PUSH, instance_6
        COPY
        PUSH, instance_6
        EXTERN, "VRCSDK3ComponentsVRCPickup.__Drop__SystemVoid"
        PUSH, GameObject_1
        PUSH, instance_8
        COPY
        PUSH, instance_8
        PUSH, instance_7
        EXTERN, "UnityEngineGameObject.__get_transform__UnityEngineTransform"
        PUSH, instance_7
        PUSH, pos
        PUSH, rot
        EXTERN, "UnityEngineTransform.__SetPositionAndRotation__UnityEngineVector3_UnityEngineQuaternion__SystemVoid"
        PUSH, leftHand
        JUMP_IF_FALSE, 0x0000023C
        PUSH, eventTarget
        PUSH, instance_9
        COPY
        PUSH, instance_9
        PUSH, eventName_0
        EXTERN, "VRCUdonCommonInterfacesIUdonEventReceiver.__SendCustomEvent__SystemString__SystemVoid"
        JUMP, 0x00000268
        PUSH, eventTarget
        PUSH, instance_A
        COPY
        PUSH, instance_A
        PUSH, eventName_1
        EXTERN, "VRCUdonCommonInterfacesIUdonEventReceiver.__SendCustomEvent__SystemString__SystemVoid"
        JUMP, 0xFFFFFFFC
    

.code_end