How to correctly indicate the date in the sitemap?

Question

Create a sitemap

Question for SEO experts. When I change one line in the header or footet (well, not very important, maybe a link), do I need to update lastmod on all pages (this applies to the server response and lastmod in sitemap.xml)?
For example, on the news page, lasmod is updated not only for the NEW news, but also for the LIST of news page, as a new one has been added.
But do I need to change the lastmod for all pages if, for example, I added news and it (the title) is visible in the sidebar on the entire site?

Answer 1

Spit.
Look at lastmode as a server load reduction and a priority in scanning.
Naturally, the more important the edit (the text of the article, the title, the time tag), the more desirable it is to update the lastmode.