CreateACronWithConfigPath

Cron_Post.php

<?php

declare(strict_types=1);

namespace MageVision\Blog89\Cron;

use Magento\Framework\App\Config\ScopeConfigInterface;
use Magento\Store\Model\ScopeInterface;

class Post
{
    public const XML_PATH_ENABLE = 'blog89/post/enabled';

    protected ScopeConfigInterface $scopeConfig;

    /**
     * @param ScopeConfigInterface $scopeConfig
     */
    public function __construct(
        ScopeConfigInterface $scopeConfig
    ) {
        $this->scopeConfig = $scopeConfig;
    }

    /**
     * Execute cron
     *
     * @return void
     */
    public function execute()
    {
        // check if enabled
        if (!$this->scopeConfig->isSetFlag(
            self::XML_PATH_ENABLE,
            ScopeInterface::SCOPE_STORE
        )
        ) {
            return;
        }

        //Add your code

    }
}

crontab.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Cron:etc/crontab.xsd">
    <group id="default">
        <job instance="MageVision\Blog89\Cron\Post" method="execute" name="magevision_blog69_post_cron">
            <config_path>crontab/default/jobs/magevision_blog89_cron/schedule/cron_expr</config_path>
        </job>
    </group>
</config>

Post.php

<?php

declare(strict_types=1);

namespace MageVision\Blog89\Model\Config\Backend;

use Magento\Cron\Model\Config\Source\Frequency;
use Magento\Framework\App\Cache\TypeListInterface;
use Magento\Framework\App\Config\ScopeConfigInterface;
use Magento\Framework\App\Config\Value;
use Magento\Framework\App\Config\ValueFactory;
use Magento\Framework\Data\Collection\AbstractDb;
use Magento\Framework\Exception\LocalizedException;
use Magento\Framework\Model\Context;
use Magento\Framework\Model\ResourceModel\AbstractResource;
use Magento\Framework\Registry;

class Post extends Value
{
    public const CRON_STRING_PATH = 'crontab/default/jobs/magevision_blog89_cron/schedule/cron_expr';

    protected ValueFactory $configValueFactory;

    /**
     * @param Context $context
     * @param Registry $registry
     * @param ScopeConfigInterface $config
     * @param TypeListInterface $cacheTypeList
     * @param ValueFactory $configValueFactory
     * @param AbstractResource|null $resource
     * @param AbstractDb|null $resourceCollection
     * @param array $data
     */
    public function __construct(
        Context $context,
        Registry $registry,
        ScopeConfigInterface $config,
        TypeListInterface $cacheTypeList,
        ValueFactory $configValueFactory,
        AbstractResource $resource = null,
        AbstractDb $resourceCollection = null,
        array $data = []
    ) {
        $this->configValueFactory = $configValueFactory;
        parent::__construct($context, $registry, $config, $cacheTypeList, $resource, $resourceCollection, $data);
    }

    /**
     * After save handler
     *
     * @return $this
     * @throws LocalizedException
     */
    public function afterSave()
    {
        $time = $this->getData('groups/post/fields/time/value');
        if (empty($time)) {
            $time = explode(
                ',',
                $this->_config->getValue(
                    'blog89/post/time',
                    $this->getScope(),
                    $this->getScopeId()
                ) ?: '0,0,0'
            );
            $frequency = $this->_config->getValue(
                'blog89/post/frequency',
                $this->getScope(),
                $this->getScopeId()
            );
        } else {
            $frequency = $this->getData('groups/post/fields/frequency/value');
        }
        $frequencyWeekly = Frequency::CRON_WEEKLY;
        $frequencyMonthly = Frequency::CRON_MONTHLY;

        $cronExprArray = [
            (int)$time[1],                                    # Minute
            (int)$time[0],                                    # Hour
            $frequency == $frequencyMonthly ? '1' : '*',      # Day of the Month
            '*',                                              # Month of the Year
            $frequency == $frequencyWeekly ? '1' : '*',       # Day of the Week
        ];

        $cronExprString = join(' ', $cronExprArray);

        try {
            $configValue = $this->configValueFactory->create();
            $configValue->load(self::CRON_STRING_PATH, 'path');
            $configValue->setValue($cronExprString)->setPath(self::CRON_STRING_PATH)->save();
        } catch (\Exception $e) {
            throw new LocalizedException(__('We can\'t save the Cron expression.'));
        }
        return parent::afterSave();
    }
}

system.xml

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:noNamespaceSchemaLocation="urn:magento:module:Magento_Config:etc/system_file.xsd">
    <system>
        <tab id="magevision" translate="label" sortOrder="1000">
            <label>MageVision Blog Posts</label>
        </tab>
        <section id="blog89" translate="label" type="text" sortOrder="1012" showInDefault="1" showInWebsite="1" showInStore="1">
            <label>Blog Post 89</label>
            <tab>magevision</tab>
            <resource>MageVision_Blog89::blog89_configuration</resource>
            <group id="post" translate="label" type="text" sortOrder="10" showInDefault="1" showInWebsite="1" showInStore="1">
                <label>Generation Settings</label>
                <field id="enabled" translate="label" type="select" sortOrder="1" showInDefault="1" showInWebsite="1" showInStore="1" canRestore="1">
                    <label>Enabled</label>
                    <source_model>Magento\Config\Model\Config\Source\Yesno</source_model>
                </field>
                <field id="time" translate="label" type="time" sortOrder="2" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Start Time</label>
                    <depends>
                        <field id="enabled">1</field>
                    </depends>
                </field>
                <field id="frequency" translate="label" type="select" sortOrder="3" showInDefault="1" showInWebsite="1" showInStore="1">
                    <label>Frequency</label>
                    <source_model>Magento\Cron\Model\Config\Source\Frequency</source_model>
                    <backend_model>MageVision\Blog89\Model\Config\Backend\Post</backend_model>
                    <depends>
                        <field id="enabled">1</field>
                    </depends>
                </field>
            </group>
        </section>
    </system>
</config>