There could be several reasons why the Order Complete email notification is not being sent.
I suggest checking if the “Order Complete” email notification is enabled in the Email settings under WooCommerce > Settings > Emails. Please ensure that the toggle button is turned on for this email notification.
If the email notification is enabled, I would recommend checking the email logs to see if any errors are being recorded. You can do this by installing the WP Mail Logging plugin. Check if there are any records of the Order Complete email notification being sent and if there are any errors reported.
Additionally, it could be worth checking your email spam/junk folders to ensure that the email is not being filtered as spam. If it is, you may need to whitelist the email sender or domain to ensure that future emails are delivered to your inbox.
You can also install an SMTP plugin, such as WP Mail SMTP. It’s the easiest way to ensure your order emails are delivered to your customer’s inbox using a third-party email service like Sendinblue.
If none of the above suggestions resolves the issue, it could be worth trying to deactivate any third-party plugins or themes interfering with the email notifications. You can also check Email FAQs here: https://woocommerce.com/document/email-faq/.
I hope this information helps to resolve your issue.