The block editor on widgets can be much slower to load and will load more requests in wp-admin so it can make it a much slower experience. When using the block editor on widgets it can be as many as 231 requests and take 2.5 seconds to load. Using the classic editor when editing widgets will be 83 requests and 1.2 seconds to load.
There are two methods to be able to restore editing widgets in wp-admin back to the classic editor the first is installing and activating the Classic Widgets plugin on your site. The plugin has no settings and only needs to be installed and activated on the site.
The second method is using the filter that is included in WordPress core to disable the block editor on widgets. MainWP has an easy-to-use code snippets extension that will allow you to execute code snippets on all connected child sites.
The code snippet to use is the following;
// Disables the block editor from managing widgets in the Gutenberg plugin.
add_filter( 'gutenberg_use_widgets_block_editor', '__return_false' );
// Disables the block editor from managing widgets.
add_filter( 'use_widgets_block_editor', '__return_false' );
Using either the plugin or the code snippets method will quickly allow your site to return to using the faster classic editor when editing widgets on your site.