Use SearchablePopupContent to show a popup with a search field input, a TreeView containing the options will be populated using parameter string[] data. Example of usage is in RoadSegmentDataDrawer.

RoadSegmentDataDrawer.cs

using JacatGames.ShapeShifting;
using UnityEditor;
using UnityEngine;

namespace JacatGames.ShapeShifting
{
    [CustomPropertyDrawer(typeof(RoadSegmentData))]
    public class RoadSegmentDataDrawer : PropertyDrawer
    {
        // You can define your dropdown options here
        private string[] _dropdownOptions;

        private string[] DropdownOptions
        {
            get
            {
                if (_dropdownOptions == null)
                {
                    _dropdownOptions = StageSetupConfig.GetConfig().SegmentsId.ToArray();
                }

                return _dropdownOptions;
            }
        }

        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        {
            EditorGUI.BeginProperty(position, label, property);

            // Drawing the label
            position = EditorGUI.PrefixLabel(position, GUIUtility.GetControlID(FocusType.Passive), label);

            // Getting the 'Id' property
            SerializedProperty idProperty = property.FindPropertyRelative("_id");

            // Checking if the property is null
            if (idProperty != null)
            {
                if (GUI.Button(position, idProperty.stringValue))
                {
                    PopupWindow.Show(position, new SearchablePopupContent(idProperty, DropdownOptions));
                }
            }

            EditorGUI.EndProperty();
        }
    }
}

SearchablePopupContent.cs

using System.Collections.Generic;
using System.Linq;
using UnityEditor;
using UnityEditor.IMGUI.Controls;
using UnityEngine;

public class SearchablePopupContent : PopupWindowContent
{
    private SerializedProperty property;
    private SearchField searchField;
    private MyTreeView treeView;
    private List<string> data;
    private bool focused;

    public SearchablePopupContent(SerializedProperty property, string[] data)
    {
        this.property = property;
        this.data = data.ToList();
        searchField = new SearchField();
        treeView = new MyTreeView(new TreeViewState(), this.data, property, this);
        treeView.Reload();
        searchField.SetFocus();
        searchField.downOrUpArrowKeyPressed += OnArrowKeyPressed;
    }

    private void OnArrowKeyPressed()
    {
        treeView.SetFocusAndEnsureSelectedItem();
    }

    public override void OnGUI(Rect rect)
    {
        Rect searchRect = new Rect(rect.x, rect.y, rect.width, 25);
        treeView.searchString = searchField.OnGUI(searchRect, treeView.searchString);

        Rect treeViewRect = new Rect(rect.x, rect.y + 25, rect.width, rect.height - 25);
        treeView.OnGUI(treeViewRect);
        
        if (Event.current.type == EventType.KeyUp && Event.current.keyCode == KeyCode.Return)
        {
            treeView.SelectItem(0);
        }
    }

    private class MyTreeView : TreeView
    {
        private List<string> data;
        private SerializedProperty property;
        private PopupWindowContent parentWindow;
        private IList<TreeViewItem> filteredItems;

        public MyTreeView(TreeViewState state, List<string> data, SerializedProperty property, PopupWindowContent parentWindow) :
            base(state)
        {
            this.data = data;
            this.property = property;
            this.parentWindow = parentWindow;
        }

        protected override IList<TreeViewItem> BuildRows(TreeViewItem root)
        {
            filteredItems = new List<TreeViewItem>();

            for (int i = 0; i < data.Count; i++)
            {
                if (string.IsNullOrEmpty(searchString) || data[i].Contains(searchString))
                {
                    filteredItems.Add(new TreeViewItem { id = i, depth = 1, displayName = data[i] });
                }
            }

            SetupParentsAndChildrenFromDepths(root, filteredItems);

            return filteredItems;
        }

        protected override void SingleClickedItem(int id)
        {
            base.SingleClickedItem(id);
            SelectItem(id);
            // var item = FindItem(id, rootItem);
            // OnSelectItem(item.displayName);
        }

        protected override TreeViewItem BuildRoot()
        {
            var root = new TreeViewItem { id = 0, depth = -1, displayName = data[0] };
            var allItems = new List<TreeViewItem>();

            for (int i = 0; i < data.Count; i++)
            {
                allItems.Add(new TreeViewItem { id = i + 1, depth = 0, displayName = data[i] });
            }

            SetupParentsAndChildrenFromDepths(root, allItems);

            return root;
        }

        public override void OnGUI(Rect rect)
        {
            base.OnGUI(rect);
            if (Event.current.type == EventType.KeyDown && Event.current.keyCode == KeyCode.Return)
            {
                // Set the value of the property when the Return key is pressed
                var selecteds = (IEnumerable<int>)GetSelection();
                if (selecteds.Count() > 0)
                {
                    int id = selecteds.First();
                    SelectItem(id);
                }
            }
        }

        public void SelectItem(int id)
        {
            // Debug.Log($"selecting:{id}");
            var item = FindItem(id, rootItem);
            // var item = filteredItems[id];
            // Debug.Log($"selected:{item.displayName}");
            OnSelectItem(item.displayName);
        }

        void OnSelectItem(string value)
        {
            property.stringValue = value;
            property.serializedObject.ApplyModifiedProperties();
            parentWindow.editorWindow.Close();
        }
    }
}