pcdr.marty

Automatically send HTTP Header “last-modified”. 
You can use post last modification time or creation date… (settings in administration)

Last modified header

Automatically send HTTP Header "last-modified".

MotoPress

This plugin allows you to optionally keep the last post modified date unchanged when you update the post in WordPress Classic Editor.
It adds datepicker and checkbox to the Publish panel of every post. If you select checkbox when you update the post, the last modified date will change; if not, this date will not change no matter how many times you update the post.
This is a helpful thing if you make only slight changes to the post and don’t want it to be noticed by the search engine crawlers or even in the post information publicly visible on your website.
Only use the plugin to keep the last modified date unchanged for minor changes. If you make a major change to a post, make sure to check the box to update the last modified date, thus making search engines aware of the update.
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<h3>Copyright</h3>
Сontrol Post Modified Date, Copyright (C) 2023, MotoPress https://motopress.com/ 
Сontrol Post Modified Date plugin is distributed under the terms of the GNU GPL.

Сontrol Post Modified Date

Keep the last modified date unchanged for minor post updates.

Last modified header vs Сontrol Post Modified Date