You already install WP Mail SMTP and email sent successfully. But Notification email still not being sent.
Then please use tnis code
<?php add_filter( 'bp_email_use_wp_mail', '__return_true' );
Put it on bp-custom.php file and upload to directory wp-content/plugins. If you dont have it yet, please create a new one.
Please try to register again. But after registration, you need to wait 1 - 5 minutes untill email activation sent to your email. because first email usually does come slower.