The expression $this->SubmittedForm()->canCreate(); of type boolean|string adds the type string to the return on line 30 which is incompatible with the return type of the parent method SilverStripe\UserForms\M...tedFormField::canCreate of type boolean.
The expression $this->SubmittedForm()->canView(); of type boolean|string adds the type string to the return on line 40 which is incompatible with the return type of the parent method SilverStripe\UserForms\M...ittedFormField::canView of type boolean.
The expression $this->SubmittedForm()->canEdit(); of type boolean|string adds the type string to the return on line 50 which is incompatible with the return type of the parent method SilverStripe\UserForms\M...ittedFormField::canEdit of type boolean.
The expression $this->SubmittedForm()->canDelete(); of type boolean|string adds the type string to the return on line 60 which is incompatible with the return type of the parent method SilverStripe\UserForms\M...tedFormField::canDelete of type boolean.