The “All Posts” page – /wp-admin/edit.php – does not show a featured image just by using WP Core. You have to add code to display featured images there. You may need to look back at your backups to see what code you were previously using to get the featured image to show up.
It could be that you edited your theme’s functions.php file, and when you updated the theme, it overwrote that file. If that’s the case, find a backup of your functions.php file with the modifications, and take a moment to create a child theme and place the code there. This way, you can update the parent theme safely, and your child theme will house all your changes so they don’t get overwritten.
It could also be that this code was built into a theme or plugin that also updated. If so, check with the theme or plugin author to see whether the feature was removed, or if perhaps there’s a new setting you need to adjust. You could consider adding a new plugin that will show the featured image in the post list – there are some available if you search.