Hello Mike,
Out of the box, our BoldGrid Themes are not able to hide the header entirely. You can add custom CSS to hide it:
.site-header {
display: none;
}
Alternatively you can use the Post and Page Builder with a non-BoldGrid theme, like the Twenty Twenty or Twenty Twenty-One default theme, and then select the Content Only page template.

Please let us know if we can help with anything else.
Thanks,
Nicole