Hello @restorm,
The Classic Widgets plugin is 2 lines of code to disable the block editor from managing the widgets. The UI itself is managed within WordPress Core but is extensible by plugins and themes.
I was curious if the problem is coming directly from WordPress Core itself. In testing WP 6.0, I wasn’t able to reproduce the problem. Here’s how I tested it:
Test 1:
Theme: Twenty Twenty-One
Plugins: only the Classic Widgets plugin activated (no other plugins)
Result: widgets UI (Appearance > Widgets) works without error
Test 2:
Theme: Twenty Twenty
Plugins: only the Classic Widgets plugin activated (no other plugins)
Result: widgets UI (Appearance > Widgets) works without error
Test 3:
Theme: Twenty Twenty-One
Plugins: Gutenberg v 13.3.0 and Classic Widgets plugin activated
Result: widgets UI (Appearance > Widgets) works without error
Test 4:
Theme: Twenty Twenty
Plugins: Gutenberg v 13.3.0 and Classic Widgets plugin activated
Result: widgets UI (Appearance > Widgets) works without error
In this testing, it does not appear the issue is coming from the Classic Widgets plugin. In a default setup, it works.
What are the next steps to help resolve whatever is going on?
I’m wondering: Is there a plugin or theme on your site that is causing a conflict or possibly a JS error?
To find out, I’d suggest starting with the 6.0 Troubleshooting guide found here https://www.ads-software.com/support/topic/read-this-first-wordpress-6-0/.
It’ll walk you through troubleshooting steps including flushing caches (caching plugins, server caching, and browser caching), deactivating all the plugins (except for the Classic Widgets plugin), troubleshooting for JS errors within your browser, and switching to the Twenty Twenty-One theme.
Why?
These steps help to identify where the problem exists on your site to direct you to where to report the issue for resolution. For example, if a plugin is causing the issue, then that plugin could be disabled for now until its author fixes whatever the issue is.