yajra datatable global filter does not use LIKE operator instead in eager loaded models

I have a Conversation model like this :

    class Conversation extends Model
    {
        protected $primaryKey = 'conversation_id';
        public function latestQuestion ()
        {
            return $this->hasOne('App\Question','conversation_id','conversation_id')
                ->orderBy('created_at', 'desc');
        }
    
    }

And a Question model like this :

    class Question extends Model
        {
            protected $primaryKey = 'question_id';
            public function conversation ()
            {
                return $this->belongsTo('App\Conversation', 'conversation_id', 'conversation_id');
            }
        }

Now I want to list all Conversations with their latest questions. for that I used yajra laravel datatables package like this :

    $('#allQuestionsTable').DataTable({
                processing: true,
                serverSide: true,
                "bSort": false,
                "responsive": true,
                ajax: {
                    url: '{!! route('admin.conversation.conversationsDatatable ') !!}'
                },
                columns: [
                    {
                        data: 'conversation_id',
                        name: 'conversation_id'
                    },
                    {
                        data: 'text',
                        name: 'latestQuestion.text'
                    },
                    {
                        data: 'created_at',
                        'searchable': false,
                        'orderable': false
                    },
                    {
                        data: 'answer',
                        name: 'latestQuestion.answer'
                    }
                });

As you can see I used latestQuestion relation to fetch text and answer fields from Question model.

Now I want user can input a word in global search filter textbox and datatable show all conversations with questions that have a text or answer field contain that word.

On the backend I wrote this :

    $conversations =
        Conversation::
        with('latestQuestion');

    $datatable = app('datatables')->of($conversations)
                    ->addColumn('checkbox', '<input type="checkbox" name="item_id[]" value="{{$conversation_id}}">')
                    ->editColumn('text', function ($conversation) {
                        $res = '<span data-toggle="tooltip" data-placement="top" title="' . str_limit(strip_tags($conversation->latestQuestion->text), 200) . '">' . str_limit(strip_tags($conversation->latestQuestion->text), 40) . '</span>';
    
                        return $res;
                    })
                    ->editColumn('answer', function ($conversation) {
                        $res = '<span data-toggle="tooltip" data-placement="top" title="' . str_limit(strip_tags($conversation->latestQuestion->answer), 200) . '">' . str_limit(strip_tags($conversation->latestQuestion->answer), 40) . '</span>';
                        return $res;
                    })
                    //other columns here 
                    ;
    
                return $datatable->make(true);

But when I tried to input a word on global textbox, datatable return all questions that have exactly that word in answer or text field means uses = operator while I want to use LIKE operator.

What do I do?