Only Admin receives email

Mail sent from WP uses wp_mail() function. There is a filter that you can use before the mail is sent to filter the arguments used in the wp_mail() function, including the $to value.

See https://developer.wordpress.org/reference/hooks/wp_mail/

Look at the example code on that page to get an idea of how to block (or redirect) all mail sent by wp_mail(). You could put your implementation of that in your Child Theme’s functions file, or your own private plugin.

It is possible that a plugin or a theme might not use the wp_mail() function, using instead mail() or their own implementation of phpMailer (which wp_mail() uses).