Since this is a theme-specific question it would be better to ask the theme’s author/support team directly. As you can see from header.php your theme uses template parts. The header-main.php file is the most likely one to contain the logo since its name implies it would be used sitewide.
You are most likely looking for code that looks something like this:
get_theme_mod('custom_logo'), 'medium')
or
if(has_custom_logo())
or
the_custom_logo()
generally – something to do with custom_logo. When you find the call to custom_logo it will probably specify medium or some other image size. You want to change whatever image size the theme is using to full which in most cases will display the full, un-resized version you uploaded. Once you’ve done that, you may also need to edit some CSS since that can also affect the size the image is displayed at – though not the actual, underlying file.