How can I

[iampedro]

I just want to open up a html file and edit it in this app without having a project is that possible?

[Pablo]

WYSIWYG Web Builder is not an HTML editor, so you cannot directly edit HTML files.
However, you can add custom code via Page HTML or an HTML object: https://wysiwygwebbuilder.com/add_html.html

[iampedro]

I would love if you could build it with split view of the code and wysiwyg builder.

[Pablo]

WYSIWYG Web Builder is not an HTML editor, the HTML code does not exist until you preview or published the page.
Therefor a split view will not be possible.