composer update symfony/flex
yarn upgrade "@symfony/webpack-encore@^0.32.0"

composer recipes:install symfony/webpack-encore-bundle --force -v

$ composer require symfony/ux-chartjs

Using version ^1.0 for symfony/ux-chartjs
./composer.json has been updated
Synchronizing package.json with PHP packages
Don't forget to run npm or yarn to refresh your Javascript dependencies!
...

// package.json
{
    "devDependencies": {
        ...
        "@symfony/ux-chartjs": "file:vendor/symfony/ux-chartjs/Resources/assets"
    }
}

// assets/controllers.json
{
    "controllers": {
        "@symfony/ux-chartjs": {
            "chart": {
                "enabled": true,
                "webpackMode": "eager"
            }
        }
    },
    "entrypoints": []
}

yarn install --force
yarn encore dev

// ...
use Symfony\UX\Chartjs\Builder\ChartBuilderInterface;
use Symfony\UX\Chartjs\Model\Chart;
class HomeController extends AbstractController
{
    /**
     * @Route("/", name="homepage")
     */
    public function index(ChartBuilderInterface $chartBuilder): Response
    {
        $chart = $chartBuilder->createChart(Chart::TYPE_LINE);
        $chart->setData([
            'labels' => ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
            'datasets' => [
                [
                    'label' => 'My First dataset',
                    'backgroundColor' => 'rgb(255, 99, 132)',
                    'borderColor' => 'rgb(255, 99, 132)',
                    'data' => [0, 10, 5, 2, 20, 30, 45],
                ],
            ],
        ]);
        $chart->setOptions([/* ... */]);
        return $this->render('home/index.html.twig', [
            'chart' => $chart,
        ]);
    }
}

{{ render_chart(chart) }}
{# You can pass HTML attributes as a second argument to add them on the <canvas> tag #}
{{ render_chart(chart, {'class': 'my-chart'}) }}