The latest WordPress core update (5.8) has come with a significant change to the widgets interface, bringing it more in line with the block editor that was introduced in WordPress 5 for pages and posts. We’ve received a number of reports that this update has made it difficult to find and edit your existing widgets and, in some cases, has caused conflicts with third-party plugins or errors in the WordPress theme customizer.
If you’d like to restore the previous widgets interface, we recommend installing the “Classic Widgets” plugin. More information about this plugin can be found here: https://wordpress.org/plugins/classic-widgets/.