Does the preview in backend configuration work? After saving CB AntiSpam parameters there should be a preview available directly under the Mode parameter as shown below.
reCaptcha v2 and v3 both appear to be working fine in my tests. Note when creating a v2 key be sure to select ""I'm not a robot" Checkbox" option. If selecting "Invisible reCAPTCHA badge" be sure in CB AntiSpam you set Mode to "reCaptcha (Invisible)" for that to work.
Furthermore we do want to have the CB Antispam field to be listed as last one on the list of fields. We are desperately trying to move it to bottom of the registration form before send button.
Field positions on registration are first ordered by the tab they're on then by their field order. So you could create a new tab to put the captcha on and position that tab last or move the captcha field to the last tab then order the captcha field to be last on that tab.