Yes, the games (tools / demos / carts / etc) that you make are your creation, that you can release with a license of your choosing. This includes program export or HTML exports that include the runtime engine part of pico-8.
See: https://www.lexaloffle.com/pico-8.php?page=faq + the license document that comes with pico-8.
Also this video that talks about more aspects of selling: https://www.youtube.com/watch?v=yKU2WWwhpQc