Modified patch of https://www.drupal.org/project/commerce/issues/3082613#comment-14787941 to apply over already applied other patches.

commerce-send_mail_after_registration_in_checkout-3082613-10-wwm-modified.patch

diff --git a/modules/checkout/config/install/commerce_checkout.commerce_checkout_flow.default.yml b/modules/checkout/config/install/commerce_checkout.commerce_checkout_flow.default.yml
index c350ab28..630c7852 100644
--- a/modules/checkout/config/install/commerce_checkout.commerce_checkout_flow.default.yml
+++ b/modules/checkout/config/install/commerce_checkout.commerce_checkout_flow.default.yml
@@ -11,6 +11,7 @@ configuration:
     login:
       allow_guest_checkout: true
       allow_registration: false
+      new_registration_mail: ''
       step: login
       weight: 0
     contact_information:
@@ -29,7 +30,10 @@ configuration:
         format: plain_text
       step: complete
       weight: 4
+    completion_register:
+      new_registration_mail: ''
+      weight: 5
     order_summary:
       view: null
       step: _sidebar
-      weight: 5
+      weight: 6
diff --git a/modules/checkout/config/schema/commerce_checkout.schema.yml b/modules/checkout/config/schema/commerce_checkout.schema.yml
index dffb610d..a323fd8d 100644
--- a/modules/checkout/config/schema/commerce_checkout.schema.yml
+++ b/modules/checkout/config/schema/commerce_checkout.schema.yml
@@ -78,6 +78,9 @@ commerce_checkout.commerce_checkout_pane.login:
     register_form_title:
       type: string
       label: 'Title For New Customer Form'
+    new_registration_mail:
+      type: string
+      label: 'Send registration email'
 
 commerce_checkout.commerce_checkout_pane.order_summary:
   type: commerce_checkout_pane_configuration
@@ -94,6 +97,13 @@ commerce_checkout.commerce_checkout_pane.completion_message:
       label: 'message'
       translatable: true
 
+commerce_checkout.commerce_checkout_pane.completion_register:
+  type: commerce_checkout_pane_configuration
+  mapping:
+    new_registration_mail:
+      type: string
+      label: 'Send registration email'
+
 commerce_checkout_pane_configuration:
   type: mapping
   mapping:
diff --git a/modules/checkout/src/Plugin/Commerce/CheckoutPane/CompletionRegister.php b/modules/checkout/src/Plugin/Commerce/CheckoutPane/CompletionRegister.php
index 3fe770ff..180c5c0b 100644
--- a/modules/checkout/src/Plugin/Commerce/CheckoutPane/CompletionRegister.php
+++ b/modules/checkout/src/Plugin/Commerce/CheckoutPane/CompletionRegister.php
@@ -136,6 +136,63 @@ class CompletionRegister extends CheckoutPaneBase implements CheckoutPaneInterfa
     );
   }
 
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+        'new_registration_mail' => '',
+      ] + parent::defaultConfiguration();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationSummary() {
+    if (!empty($this->configuration['new_registration_mail'])) {
+      $summary = '<br>' . $this->t('Registration: Send new account email (' . $this->configuration['new_registration_mail'] . ')');
+    }
+    else {
+      $summary = '<br>' . $this->t('Registration: Do not send new account email');
+    }
+
+    return $summary;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    $form = parent::buildConfigurationForm($form, $form_state);
+    $config_notify = \Drupal::configFactory()->get('user.settings')->get('notify');
+    $form['new_registration_mail'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Send email after registration?'),
+      '#options' => array_merge(['' => 'Do not send'], array_combine(array_keys($config_notify), array_keys($config_notify))),
+      '#default_value' => $this->configuration['new_registration_mail'],
+      '#states' => [
+        'visible' => [
+          ':input[name="configuration[panes][login][configuration][allow_registration]"]' => ['checked' => TRUE],
+        ],
+      ],
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    parent::submitConfigurationForm($form, $form_state);
+
+    if (!$form_state->getErrors()) {
+      $values = $form_state->getValue($form['#parents']);
+      $this->configuration['new_registration_mail'] = $values['new_registration_mail'];
+    }
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -263,6 +320,9 @@ class CompletionRegister extends CheckoutPaneBase implements CheckoutPaneInterfa
       $form_state->setRedirectUrl($url);
     }
     $this->messenger()->addStatus($this->t('Registration successful. You are now logged in.'));
+    if (!empty($this->configuration['new_registration_mail'])) {
+      _user_mail_notify($this->configuration['new_registration_mail'], $account);
+    }
   }
 
 }
diff --git a/modules/checkout/src/Plugin/Commerce/CheckoutPane/Login.php b/modules/checkout/src/Plugin/Commerce/CheckoutPane/Login.php
index aecb96a6..3fcc7bd3 100644
--- a/modules/checkout/src/Plugin/Commerce/CheckoutPane/Login.php
+++ b/modules/checkout/src/Plugin/Commerce/CheckoutPane/Login.php
@@ -144,6 +144,7 @@ class Login extends CheckoutPaneBase implements CheckoutPaneInterface, Container
       'registration_form_mode' => 'register',
       'returning_customer_form_title' => '',
       'register_form_title' => '',
+      'new_registration_mail' => '',
     ] + parent::defaultConfiguration();
   }
 
@@ -173,6 +174,13 @@ class Login extends CheckoutPaneBase implements CheckoutPaneInterface, Container
       $summary .= $this->t('Title For New Customer Form: ') . $this->configuration['register_form_title'] . '<br>';
     }
 
+    if (!empty($this->configuration['new_registration_mail'])) {
+      $summary .= '<br>' . $this->t('Registration: Send new account email (' . $this->configuration['new_registration_mail'] . ')');
+    }
+    else {
+      $summary .= '<br>' . $this->t('Registration: Do not send new account email');
+    }
+
     return $summary;
   }
 
@@ -212,6 +220,18 @@ class Login extends CheckoutPaneBase implements CheckoutPaneInterface, Container
       '#title' => $this->t('Title For New Customer Form'),
       '#default_value' => $this->configuration['register_form_title'],
     ];
+    $config_notify = \Drupal::configFactory()->get('user.settings')->get('notify');
+    $form['new_registration_mail'] = [
+      '#type' => 'select',
+      '#title' => $this->t('Send email after registration?'),
+      '#options' => array_merge(['' => 'Do not send'], array_combine(array_keys($config_notify), array_keys($config_notify))),
+      '#default_value' => $this->configuration['new_registration_mail'],
+      '#states' => [
+        'visible' => [
+          ':input[name="configuration[panes][login][configuration][allow_registration]"]' => ['checked' => TRUE],
+        ],
+      ],
+    ];
 
     return $form;
   }
@@ -229,6 +249,7 @@ class Login extends CheckoutPaneBase implements CheckoutPaneInterface, Container
       $this->configuration['registration_form_mode'] = $values['registration_form_mode'];
       $this->configuration['returning_customer_form_title'] = $values['returning_customer_form_title'];
       $this->configuration['register_form_title'] = $values['register_form_title'];
+      $this->configuration['new_registration_mail'] = $values['new_registration_mail'];
     }
   }
 
@@ -461,6 +482,9 @@ class Login extends CheckoutPaneBase implements CheckoutPaneInterface, Container
         if (!$form_state->hasAnyErrors()) {
           $account->save();
           $form_state->set('logged_in_uid', $account->id());
+          if ($this->configuration['allow_registration'] && !empty($this->configuration['new_registration_mail'])) {
+            _user_mail_notify($this->configuration['new_registration_mail'], $account);
+          }
         }
         break;
     }