AddACustomSession

di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <virtualType name="MageVision\Blog43\Model\Session\Storage" type="Magento\Framework\Session\Storage">
        <arguments>
            <argument name="namespace" xsi:type="string">blog43</argument>
        </arguments>
    </virtualType>
    <type name="MageVision\Blog43\Model\Session">
        <arguments>
            <argument name="storage" xsi:type="object">MageVision\Blog43\Model\Session\Storage</argument>
        </arguments>
    </type>
</config>

Session.php

<?php
namespace MageVision\Blog43\Model;

use Magento\Framework\Session\SessionManager;

/**
 * Blog43 session model
 */
class Session extends SessionManager
{
}

TestBlockClass.php

<?php
namespace MageVision\Blog43\Block;

use Magento\Framework\View\Element\Template;
use MageVision\Blog43\Model\Session;

class TestBlockClass extends Template
{
    /**
     * @var Session
     */
    protected $session;

    /**
     * @param Session $productOptionFactory
     */
    public function __construct(
        Session $session
    ) {
        $this->session = Session;
    }
  
    public function sessionData()
    {
        $this->session->setData('custom', 'value');
        $this->session->getData('custom');
        $this->session->unsetData('custom');
    }
  
}