OK

All template parts from inc folder is working from child themes if you
place them in the same folder structure

I managed to solve it, I placed the header.php file in my child theme and made the inclusion in it using the correct function

You should have used this get_template_part( ) function to include headers and not include it.

I am using a child theme and it is useless to put the modified files in the INC folder because the WP cannot find them

I’m customizing for a client, he bought it, it is activated, we have a license, if you give me a tip I think I can solve it, for our type of business it is not interesting that everyone can send offers