If you want to add a privacy checkbox field for your policy or for GDPR or for other reasons then you need to follow the easy steps below:
Go to form > settings and check which list is linked to your form
Go to lists click on the list name then click on custom fields
Click "New custom field"
Let's see you want to add a consent message like: " I have read and agree terms policy" where you can add your terms link.
Add the following:
-in the label you add this: I have read and agree <a href="link_terms_policy" target="_blank">terms policy</a>
-Slug: add consent
6. Click "Add"
7. Go to your form and click on "+"
8. Map it with the checkbox field
9. Click on "Save form"
10. To view the checkbox click on "preview" blue button at the left side