Using a field "send copy to myself"

Why not use the Mail 2 field and set the destination to the <[your-email]> so they get a copy by default? You could add a note saying that a copy is sent if you like. You can add a custom thank you message or whatever you want.

https://contactform7.com/setting-up-mail/

Thanks for your answer!

I think I understand what you mean but what I would like is that the person who is filling out the form can check a checkbox with the text “I want to receive a copy of this form” and if this person is checking this checkbox, he will receive a copy.

Is this also possible?

Why not offer a copy as a matter of courtesy? If you want it to be conditional, based on the use of a checkbox, you might need to use some jQuery.
Maybe someone else knows better?