Using filter to override “get_parent_theme_file_path” in child-theme

WordPress applies ltrim on the $file — ltrim( $file, "https://wordpress.stackexchange.com/" ), so it becomes inc/template-tags.php instead of /inc/template-tags.php.

So within your filter callback, you should use:

if ( $file !== 'inc/template-tags.php' )

UPDATE

my child version has the adjustments

I don’t know if you made adjustments to pluggable or non-pluggable function(s) in the template file, but as pointed by @JacobPeattie, you should consider extending parent theme functions like so:

• For pluggable functions such as twentyseventeen_posted_on, just copy the whole code and paste it in your functions.php file. And then just make your adjustments.

  Pluggable functions are defined like so, where the function is wrapped inside a conditional which checks whether a function with the same name already exists or not, and if not, the function is defined:

  if ( ! function_exists( 'function_name' ) ) :
      function function_name() {
          ...
      }
  endif;
  

• For non-pluggable functions such as twentyseventeen_front_page_section, follow the same steps above (copy the function code to your functions.php file), but make sure to rename the function — e.g. my_theme_front_page_section or my_twentyseventeen_front_page_section.

  And after you renamed the function, make sure to change the name in template files where the function is being called. For example, twentyseventeen_front_page_section is being called in the front page (front-page.php) template, so you’d change twentyseventeen_front_page_section( null, $i ); to my_theme_front_page_section( null, $i ); (if you renamed the function to my_theme_front_page_section).

I could understand that it might be a hassle to do the renaming part, but particularly for pluggable functions, you don’t need to override the template file using the parent_theme_file_path filter (or similar filter). The function(s) you’re trying to modify might also actually have filters you can simply hook into to customize/change the function output, so be sure to check that. 🙂