Hi, you could probably use the shortcode. Check out the source here: https://github.com/hCaptcha/hcaptcha-wordpress-plugin
Actually it is coded in such a way that the captcha is added to every CF7 form even if it does not contain the [cf7-hcaptcha] shortcode.
Does this make sense in a way that I am overlooking? Otherwise, I would suggest adding a new parameter to the plugin settings, something like:
Enable Contact Form 7 Addon (all forms)
Enable Contact Form 7 Addon (only based on shortcode)
Besides that, a new field type “hCaptcha” ought to be added to the CF7 form constructor GUI. Not sure if CF7 supports that. Alternatively, it should at least be documented that there are shortcodes. I had no idea it does.