Vaadin's RichTextEditor does not have label, errorText, invalid styles and helperText. CustomField is the simplest way to add those, here is example RteField

RichTextEditorView.java

package com.example.application.views;

import org.jsoup.Jsoup;
import org.jsoup.nodes.Document;

import com.vaadin.flow.component.Html;
import com.vaadin.flow.component.checkbox.Checkbox;
import com.vaadin.flow.component.customfield.CustomField;
import com.vaadin.flow.component.orderedlayout.VerticalLayout;
import com.vaadin.flow.component.richtexteditor.RichTextEditor;
import com.vaadin.flow.data.binder.Binder;
import com.vaadin.flow.router.Route;

@Route(value = "rich-text", layout = MainLayout.class)
public class RichTextEditorView extends VerticalLayout {

    public RichTextEditorView() {
        setMargin(true);
        setSpacing(true);
        var rteField = new RteField();
        rteField.setLabel("Html");
        rteField.setHelperText("Input something");
        var binder = new Binder<Data>();
        binder.forField(rteField).asRequired("Required")
                .withValidator(
                        value -> Jsoup.parse(value).select("strong").size() > 0,
                        "Bold required")
                .withValidator(
                        value -> Jsoup.parse(value).select("h1").size() > 0,
                        "H1 required")
                .bind(Data::getHtml, Data::setHtml);
        var html = new Html("<div></div>");
        binder.addValueChangeListener(e -> {
            html.setHtmlContent(
                    String.format("<div>%s</div>", rteField.getValue()));
        });

        var readOnly = new Checkbox("ReadOnly");
        readOnly.addValueChangeListener(
                e -> rteField.setReadOnly(e.getValue()));
        var disabled = new Checkbox("Disabled");
        disabled.addValueChangeListener(
                e -> rteField.setEnabled(!e.getValue()));
        add(readOnly, disabled, rteField, html);
    }

    public class Data {
        private String html;

        public String getHtml() {
            return html;
        }

        public void setHtml(String html) {
            this.html = html;
        }
    }

    public class RteField extends CustomField<String> {

        private RichTextEditor rte;

        public RteField() {
            rte = new RichTextEditor();
            add(rte);
        }

        @Override
        public void setReadOnly(boolean readOnly) {
            rte.setReadOnly(readOnly);
        }

        @Override
        public void onEnabledStateChanged(boolean enabled) {
            rte.setEnabled(enabled);
        }

        @Override
        public void setInvalid(boolean invalid) {
            // Use these in styles.css:
            //
            // vaadin-rich-text-editor[invalid] {
            //   border: 1px solid var(--lumo-error-color);
            //   background: var(--lumo-error-color-10pct);
            // }
            super.setInvalid(invalid);
            if (invalid) {
                rte.getElement().setAttribute("invalid", "");
            } else {
                rte.getElement().removeAttribute("invalid");
            }
        }

        @Override
        public boolean isEmpty() {
            Document document = Jsoup.parse(getValue());

            // Get non-normalized text including spaces and newlines
            // Note that <br>s count as newlines
            String text = document.body().wholeText();

            // Remove first newline occurrence as Quill editor adds a single
            // <br> in
            // every element even without the user having typed anything
            text = text.replaceFirst("\n", "");

            boolean hasText = !text.isEmpty();
            boolean hasImages = document.selectFirst("img") != null;

            return !hasText && !hasImages;
        }

        @Override
        public String getEmptyValue() {
            // If current value is satisfying isEmpty condition, use it to
            // satisfy Binder's asRequired.
            return isEmpty() ? getValue() : "";
        }

        @Override
        protected String generateModelValue() {
            return rte.getValue();
        }

        @Override
        protected void setPresentationValue(String newPresentationValue) {
            rte.setValue(newPresentationValue);
        }

    }
}