Revisions deos not work on the new update of wordpress 2018 ( WordPress 4.9.5.) .Went to Screen Options but does not appear

I think that revisions are disabled by default in the latest WP (but can’t guarantee that).

I do know that if you want to enable revisions, then change an value in the wp-config.php file:

define( 'WP_POST_REVISIONS', 3 );

That will save the last 3 revisions. Turn if off with a value of 0 or false. Save unlimited revisions with a value of -1. See https://codex.wordpress.org/Revisions

Once revisions are enabled, you should be able to show revisions with the ‘Screen’ options on the post/page editor screen.