web_techsystech/web_responsive/static/src/xml/discuss.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!-- Copyright 2019 Tecnativa - Alexandre Díaz
     License LGPL-3.0 or later (http://www.gnu.org/licenses/lgpl). -->
<template>
    <t t-extend="mail.discuss.ControlButtons">
        <t
            t-jquery=".o_mail_discuss_button_multi_user_channel"
            t-operation="attributes"
        >
            <attribute name="class" t-translation="off">
                btn btn-secondary o_mail_discuss_button_multi_user_channel d-md-block
                d-none
            </attribute>
        </t>
    </t>
</template>