Error in widget editor

Hello @grudzinski

Thank you for reaching out and I am happy to assist you with this.
Removing W3TC can’t cause problems, however, it’s so powerful that it can hide potential issues 🙂
All jokes aside, it seems that the issue is caused by your theme or some plugin you are using.
Switching to the default theme and disabling the plugins one by one can identify what is causing the problem.
The potential issue is when the theme or a plugin includes any blocks that haven’t changed to use the block-editor packages and still refer to the editor package then it will trigger the notice you see on the block widgets screen.
You can check more in the links below:
https://ww.wp.xz.cn/support/topic/error-in-widgets-with-new-wordpress-version-5-8-wp_enqueue_script-and-wp/#post-15090381

The Block Editor JavaScript module in 5.2

To confirm, this is not specifically related to the W3TC.

I hope this helps!