Step #1 - Create a pair of reCAPTCHA keys called a Site key and Secret key.
First login to your Google Account (Gmail) and then open the reCAPTCHA website:
https://www.google.com/recaptcha/
Then click the button labeled “Admin console”:
After logging in using your Google account you will see the reCAPTCHA Admin console. API keys are assigned per website domain. Click the plus icon located in the blue bar at the top right of the page:
Fill out the form making sure to choose reCAPTCHA version 3 and then click the Submit button:
After submitting the form you will be redirected to a page that provides your Site key and Secret key:
Step #2 - Create a new reCAPTCHA integration account in Divi Contact Form Module or Optin Module
Edit the Contact Form Module or Optin Module and enable the Content > Spam Protection > Use A Spam Protection Service
Click on the "ADD" button to create a new Spam Protection integration
3. Assign a label for the reCAPTCHA integration (use only English alphabet letters, no spaces or special characters) and Copy/Paste the reCAPTCHA keys (generated Step #1) into the appropriate fields in your Divi module settings.:
Optionally you can set the "Minimum Score" - base recommended value is 0.5 (sensitivity of detection).