Here is a Corousel widget that is an extension of yii\bootstrap5\Carousel, to show image thumbnails as indicators for the carousel.

Here is the widget code. <?php namespace app\widgets; use Yii; use yii\bootstrap5\Html;

class Carousel extends \yii\bootstrap5\Carousel {

public $thumbnails = [];

public function init()
{
    parent::init();     
    Html::addCssClass($this->options, ['data-bs-ride' => 'carousel']);
    if ($this->crossfade) {
        Html::addCssClass($this->options, ['animation' => 'carousel-fade']);
    }
}

public function renderIndicators(): string
{
    if ($this->showIndicators === false){
        return '';
    }
    $indicators = [];
    for ($i = 0, $count = count($this->items); $i < $count; $i++){
        $options = [
            'data' => [
                'bs-target' => '#' . $this->options['id'],
                'bs-slide-to' => $i
            ],
            'type' => 'button',
			'thumb' => $this->thumbnails[$i]['thumb']
        ];
        if ($i === 0){
            Html::addCssClass($options, ['activate' => 'active']);
            $options['aria']['current'] = 'true';
        }       
		
		 $indicators[] = Html::tag('li',Html::img($options['thumb']), $options);
    }
    return Html::tag('ol', implode("\n", $indicators), ['class' => ['carousel-indicators']]);
} }