There is such a form, forum reply. It is huge and I tried to shorten it to show its essence, where there is a quote. There is also a submit button that is not shown.
It is absolutely unclear how to insert text into such a form and where to insert it?
I tried inserting text into textarea name=“message_html”>, but I get ElementNotInteractableException i.e.

Element <textarea name=”message_html“> is not reachable by keyboard.

<form action="/threads/somecoolthread.908787612/add-reply" method="post" class="block js-quickReply" data-xf-init="attachment-manager quick-reply ajax-submit draft" data-draft-url="threads/somecoolthread.908787612/draft" data-draft-autosave="60" data-captcha-context="xf_guest_thread_quick_reply"
data-message-container="div[data-type='post'] .js-replyNewMessageContainer">
    <input type="hidden" name="_xfToken" value="2409434567,26f1433a729b2c456f2617f2e9d8c345a">
    <div class="message-editorWrapper">
        <script class="..." type="...">...</script>
        <div class="fr-box bbWrapper fr-ltr fr-basic fr-top" role="application" data-size="XL">
            <div class="fr-wrapper" dir="ltr" style="max-height: 150px; overflow: auto;">
                <div class="fr-element fr-view fr-element-scroll-visible" dir="ltr" contenteditable="true" style="min-height: 100px;" aria-disabled="false" spellcheck="true">
                    <blockquote data-quote="Chat" data-source="post: 4567456" data-attributes="member: 35467345">
                        <p>&ZeroWidthSpace;newetherless
                            <br>
                        </p>
                    </blockquote>
                    <p>
                        <br>
                    </p>
                </div>
            </div>
            <div class="fr-second-toolbar"></div>
        </div>
        <textarea name="message_html" class="input js-editor u-jsOnly" data-xf-init="editor" data-original-name="message" data-buttons-remove="xfInsertGif,xfCustom_parsehtml" style="height: 137px; display: none;" aria-label="Rich text box" data-min-height="100"
        placeholder="Write your reply..." data-deferred="off" data-xf-key="r" data-preview-url="threads/somecoolthread.908787612/reply-preview"><blockquote data-quote="Chat" data-source="post: 4567456" data-attributes="member: 35467345"><p>General idea</p></blockquote><p></p></textarea>
        <input type="hidden" value="[QUOTE="Chat, post: 4567456, member: 35467345"]
General idea
[/QUOTE]" data-bb-code="message">
        <noscript>
            <textarea name="message" class="input" aria-label="Rich text box">[QUOTE="Chat, post: 4567456, member: 35467345"] General idea [/QUOTE]
            </textarea>
        </noscript>
    </div>
</form>

So, how to insert text into such a form? (I think there will be no problem to click the submit button.)