Good Morning Denis,
That’s a great question. The purpose of CAPTCHA is to keep spam bots out. The downside is it also knocks out a good percentage of humans too just because it’s so reviled.
Have you tried a plugin called Cookies for Comments? It uses a cookie that’s set on your visitors browser when they visit a page. Spam bots don’t wait to submit a comment like a person who is reading the post. So the cookie keeps track of how long they’ve been on that post. If they comment before the time allowed, they’ll get a message and it’ll be rejected.
I set my threshold at six seconds and have yet to have a spam comment make it through to me since I started with the plugin months ago.
You might try that as an alternative to CAPTCHA. If you need to go with CAPTCHA, there may be a plugin out there for that. It’s not something I’ve searched for so I don’t have any recommendations there.
Enjoy your Saturday,
Bill