WP showing “warning: call_user_func_array()”, What to do?

The error you’re getting is showing, because somewhere on your site (your theme or one of your plugins) is registering a filter function that doesn’t exist.

Somewhere in your code, there will be such line (or similar to it):

add_filter( 'rewrite_rules_array', 'disable_embeds_rewrites' );

It may use different hook, so it may also look like:

add_filter( 'XXX', 'disable_embeds_rewrites' );

The problem is that the function disable_embeds_rewrites doesn’t exist on your site.

The easiest/quickest way to fix it is to remove the line above.

PS. But you should be careful. Maybe that filter is needed on your site. So when you find it, you should contact the author of that part of code (plugin/theme) and report it as a bug.