Consider providing the option for use of hCaptcha, as an alternative to Google's reCaptcha.
Alternatively, a pull-request can be made for the WordPress hCaptcha plugin here, to include s2Member support via it. The advantage here is this plugin already provides hCaptcha functionality for the rest of the website.
EXPLANATION OF THE ISSUE
Consider providing the option for use of hCaptcha, as an alternative to Google's reCaptcha.
Alternatively, a pull-request can be made for the WordPress hCaptcha plugin here, to include s2Member support via it. The advantage here is this plugin already provides hCaptcha functionality for the rest of the website.