How to Add a Custom Button to Admin Sales Order View in Magento2

1. Create a plugin in Company/Module/etc/adminhtml/di.xml

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Magento\Backend\Block\Widget\Button\Toolbar">
        <plugin name="Company_Module::pluginBefore" type="Company\Module\Plugin\PluginBefore" />
    </type>
</config>

2. Then in Company/Module/Plugin/PluginBefore.php

<?php
namespace Company\Module\Plugin;
class PluginBefore
{
    protected $view;
    public function __construct(
        \Magento\Sales\Block\Adminhtml\Order\View $view
    )
    {
        $this->view = $view;
    }
    public function beforePushButtons(
        \Magento\Backend\Block\Widget\Button\Toolbar\Interceptor $subject,
        \Magento\Framework\View\Element\AbstractBlock $context,
        \Magento\Backend\Block\Widget\Button\ButtonList $buttonList
    ) {
        $orderIds = $this->view->getOrderId();
        $message = 'Are you sure you want to do this?'.$orderIds;
        $this->_request = $context->getRequest();
        if($this->_request->getFullActionName() == 'sales_order_view'){
            $buttonList->add(
                'mybutton',
                [
                    'label' => __('Update Log'),
                    'onclick' => "confirmSetLocation('{$message}','{}')",
                    'class' => 'go'
                ],
                -1
            );
        }
    }
}

3. Clear Magento cache and run update command

php bin/magento setup:upgrade

4. Finally you will see the button in backened