For a client I used a free WordPress plugin WP Forms [1], for free you can create unlimited forms, receive unlimited messages, build forms with a nice UI [2] and you own all the data/don't call third party services. Recommended.
Yes, it works only on WordPress, in my use case, my client had a non-WordPress site, and we make a Help site on help.domain.com with WordPress, and the contact form on help.domain.com/contact.