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I don't want to dissuade you from porting it, but wanted to raise awareness of https://github.com/backdrop-contrib/turnstile which is a great alternative. Have you tried it? It works a bit like a captcha but less intrusive.

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Yes, thanks!  I had period at the end of the sentence, and it made url incorrect in my post (fixed it now)

@herb, thanks a lot, I was not aware of this option!  We will test it asap. 

Thanks a lot, Irina

Hi Deep, we are using https://github.com/backdrop-contrib/turnstile  for now, and it works for us so far.   One advantage of porting reCaptcha V3 would be to make it available for those who are not aware of Tunstile and are looking for "standard" captcha solution.    I might come back to question of porting reCaptchaV3 next year, but for now we are all set.  

Optionally, I was thinking of starting a module to accommodate a reference to turnstile in BackdropUpgrade module. 

Thanks, Irina