This seemed the best thread to ask this question:
Is there a technical issue that prevents reCaptcha v3 from being used in SMF 2.1? It seems it would be preferable, as it's less annoying to users.
Or is there something undesirable regarding v3 resulting in a deliberate choice to not use it and only support v2?
Just curious. I have it (v2) working at the moment. Thanks!