I read in another topic that the Prove Your Human captcha on the Login Page is coming from a Jetpack hook, and that wpforo does not use "Prove your Human". (Relevant Topic/Solved: https://wpforo.com/community/how-to-and-troubleshooting-2/how-can-i-remove-prove-your-humanity-from-my-login-and-register-page/#post-23381)
Short of disabling Jetpack is there a way to resolve this so the wpforo Login page shows the google recaptcha and not the Prove your Human captcha?
wpForo has built-in Google reCAPTCHA. All settings are available in Dashboard > Forums > Tools > Antispam admin page.
Great! I just set the wpForo Login Form recaptcha to YES and that solved the problem. (I thought I had already done that earlier.)