Q. Is there an alternative to using Google reCaptcha for User Registration?

Yes there is.

Some customers have problems with self-registration for users in China, when User Authentication settings including Google reCaptcha.

We now offer hCaptcha as an alternative which has been tested and verified for use in China.

This can be setup in your Settings > User Authentication > Captcha

Or switch to by Invitation only

Alternatively to avoid this issue completely disable self registration in Settings > User Authentication, then switch Captcha to none.

Then you will have to explicitly invite users to add any users at all.