how to auto clear cache after publish or update a post

add_action( 'save_post', 'wp_cache_flush' );

This should be added to the wp-config file. Right??

No, actions need to be added to your theme’s functions.php file.

Apologies for resurrecting (but I felt this was related). Can the flush be done for the specific page / post / url as such? So that the entire cache isnt being flushed.

Yeah, you can add wp_cache_flush to any hooks to flush your cache. Not recommended tho. It would unnecessarily flush other data.

What happened is when I publish a new post it doesn’t appear on the top of the home page until I flush the cache from the redis plugin setting and I’m doing it every time I publish a post.

That’s a theme/plugin issue not clearing the cached key properly.