How do I override template-tags.php in 2021 theme

Notice how the parent theme checks if they are already defined e.g.

if ( ! function_exists( 'twenty_twenty_one_entry_meta_footer' ) ) {
   ...
}

Then just define them in your child theme’s functions.php file, to override the corresponding template tag.

It should work because the child theme’s functions.php file is loaded before the parent’s functions.php file that loads:

// Custom template tags for the theme.
require get_template_directory() . '/inc/template-tags.php';