reCaptcha is pretty easy for a bot to beat these days. Maybe try switching to internal code based captcha or adjusting its "Score Threshold" to be more aggressive? We use internal captcha and have more success with it since we can change it regularly to trip up the bots. In a future release we'll also provide hCaptcha and Cloudflare Turnstile, but honestly I doubt they'll do much better.

Additionally if your forums are Kunena we provide a forum antispam plugin with CB AntiSpam to blocks bots from spamming links on the forums. It will only allow external links after a posting threshold.

I also recommend using mod_security and using an aggressive filter list. That often can catch a lot of bad actors including bots.

CB AntiSpam can IP block. In addition to blocking entire ranges of IP addresses. It's typically best to do that server side to stop them from ever reaching your site, but you can configure it from CB AntiSpam as well if you want to quick test blocking a range of IP addresses if you think there's a range specifically targeting you.

Unfortunately AI bots can basically beat any registration requirements. There isn't much more you can do about it I'm afraid.