Hello @KerryG

This feature is not built in because in most case <head> is sufficient. If you want to add some script to a limited number of page/posts then use standard wp_footer along with is_single or is_singular.

I could help better if you share the code you want to add.

Or read the following to figure out yourself:
https://developer.wordpress.org/reference/functions/is_single/
https://codex.wordpress.org/Plugin_API/Action_Reference/wp_footer