How to get all store ids assigned to specific website Magento 2?

You can get all the stores id assigned to Specific website Using Magento 2.

Retrieve the Store website relation by the website id to fetch the number of store a specific website has available.

Useful Interface class:
Magento\Store\Api\StoreWebsiteRelationInterface

Let’s Consider Base(id 1) website with two stores available,
1. English Store. (id 3)
2. French store. (id 4)

<?php
namespace Jesadiya\GetStore\Model;

use Exception;
use Psr\Log\LoggerInterface;
use Magento\Store\Api\StoreWebsiteRelationInterface;

class StoreId
{
    /**
     * @var LoggerInterface
     */
    private $logger;

    /**
     * @var StoreWebsiteRelationInterface
     */
    private $storeWebsiteRelation;

    public function __construct(
        LoggerInterface $logger,
        StoreWebsiteRelationInterface $storeWebsiteRelation
    ) {
        $this->logger = $logger;
        $this->storeWebsiteRelation = $storeWebsiteRelation;
    }

    /**
     * Get store ids from the website
     *
     * @return array
     */
    public function getStoreIds()
    {
        $storeId = [];
        $websiteId = 1; //website id
        try {
            $storeId = $this->storeWebsiteRelation->getStoreByWebsiteId($websiteId);
        } catch (Exception $exception) {
            $this->logger->error($exception->getMessage());
        }

        return $storeId;
    }
}

Call from the class,
echo $getStoreIds = $this->getStoreIds();

Output: Array of store ids.

Array
(
    [0] => 3
    [1] => 4
)

Result will be all the store id to the website in system.