Even with changing the admin area URL still we're getting hundred of daily brute force attacks and even with WHMCS builtin auto ban feature, it would be good to integrate Google recaptcha for admin area so we can get rid of these brute-force attacks for good.
Please support us till get this feature in the new updates.
Version 7.7 has now reached public beta, which includes this feature: https://preview.whmcs.com
The documentation for these new options has been published at https://docs.whmcs.com/Google_reCAPTCHA
Please join us during the pre-release testing period and provide your feedback in our dedicated beta community board: https://whmcs.community/forum/462-v77-beta-discussion/