How to add a last updated date to blog post?

Hi there,

I'm not exactly sure I fully understand.

Are you pertaining to adding the string "Last updated"?

If yes, assuming your posts have an actual modified date value, you can try the CSS provided here:
https://docs.generatepress.com/article/show-the-updated-post-date/

But if you have other concerns like making sure the string shows on Google search results, try this
https://generatepress.com/forums/topic/google-search-results-updated-date/#post-1907555

Or perhaps you're trying to show both the publish date and modified date? Let us know.