This feature has been added to Divi! Yay!
Add a Google reCAPTCHA to the Divi Contact Form.
Recommended Guide:
How To Add Google reCAPTCHA in Divi
Total 287 Votes
100%
But is there a non-paid solution?
I think, no.
None that we know of at this time. Please ask Elegant Themes to add this feature.
This plugin works for me with Divi v3.26.6