How to Customize Header and Footer with Elementor in a Theme Without Site Editor Support

Problem:

I'm using a custom theme that doesn't support the Wordpress Site Editor. I want to create a new splash page with a modified header and footer that hides the nav menu. Elementor is enabled.

Question:

How can I use Elementor to edit the existing header and footer templates from my theme and conditionally hide the nav menu for the splash page?

Additional Details:

1. Theme: custom_theme
2. Elementor Version: 3.23.4
3. WordPress Version: 6.5.5