All pages, except the homepage, have a Single Page Template which defines the consistent design & layout of all associated pages.
You can edit globally the pages' design, layout, structure, by editing the Single Page Template
The Single Page Template contains static text or dynamic tags https://developers.elementor.com/docs/dynamic-tags/
In this case, they pull the individual content from each page. You must edit them on the page, not in the template; otherwise, it will break the template and affect all pages and posts connected with the template pages / posts. These are usually the Page's title, excerpt, featured image, and custom fields.
Click on "Edit Page" link of the page. Edit the Title, Custom Fields, Excerpt and Featured image:
Troubleshooting
If you don't see the page's Custom Fields, click on Preferences > Panels > Additional > turn on the "Custom Fields" toggle:
When you click "Edit with Elementor" of a page/post, you must edit only the content, available in the Navigator: https://elementor.com/help/navigator/ , DON'T click on the Single Page Template / Single Post Template, etc. since it will affect all the connected with the template pages / posts.
Please check these guides for further information:
https://elementor.com/help/elementors-theme-builder/