Fatal error: Trait "Drupal\paragraphs\Plugin\Field\FieldWidget\FieldWidgetTrait" not found

There is no FieldWidgetTrait in this project. you might be using patches that don't properly apply or something like that.

Automatically closed - issue fixed for 2 weeks with no activity.

I was having the same issue, which occurred because I applied one of the patches in 🐛 Integrity constraint violation: 1048 Column 'langcode' cannot be null Fixed .

Since that issue is fixed and released, this patch is no longer necessary.