[[!SPForm? &requireVerify=`1` &useMathString=`1`]]
It appears that the file assets/components/captcha/captcha.php is missing. Did you install the Captcha extra?
Is that file where it's supposed to be?
Sorry for my delay if you mean by extra yes, I download the one called Captcha version 3.3.2pl
@Izumi you can check by going into files in the manager, (the third tab) that's where the assets are located.
So, find assets and go into components>captcha and see if the captcha.php is in there. If not you can manually copy and paste it in there, I think you can download the extra to your computer and get the captcha.php file in there.
Also a note, I just pulled this off of twitter, an updated captcha solution, I don't know if its useful for you or not
https://sepiariver.com/modx/recaptchav2-supports-recaptchav3/
Sorry for my delay if you mean by extra yes, I download the one called Captcha version 3.3.2pl
You downloaded it, but did you install it in Package Manager? Installation should have put that file in place. Since it was missing, it's likely that other Captcha files are missing as well.