Last Updated Without Plugin

Well, I don’t think that’s recommended because when you upgrade version, you will overwrite any changes made to core files.

Anyways, here are some guides that will help you with that:

https://www.wpbeginner.com/wp-tutorials/display-the-last-updated-date-of-your-posts-in-wordpress/

https://wphacks.com/how-to-show-last-modified-wordpress-post/

Thanks will check this out. I guess if I use a child theme, then the code won’t be erased with each update.