non-wp landing page in root with wp subdirectory

Hi! Looking to implement an existing non-wp landing page on my site. I already have wp installed in its own subdirectory (
I can get the main non-wp page working. Any pages I attempt to create in wp defaults to the main non-wp page, whether preview, or published. I have attempted to alter the .htaccess on the root, but anything I do creates a 404 or 500 error. Same with attempting to use /%postname%/ as a permalink, as in This is also results in a 404 error. When I used default naming, at least the main page would show.