social/mail_activity_team/views/mail_activity_views.xml

<?xml version="1.0" ?>
<odoo>

    <record id="mail_activity_view_form_popup" model="ir.ui.view">
        <field name="name">mail.activity.view.form.popup</field>
        <field name="model">mail.activity</field>
        <field name="inherit_id" ref="mail.mail_activity_view_form_popup" />
        <field name="arch" type="xml">
            <field name="user_id" position="attributes">
                <attribute
                    name="attrs"
                >{'invisible': [('team_id', '!=', False)]}</attribute>
            </field>
            <field name="user_id" position="after">
                <field
                    name="team_user_id"
                    attrs="{'invisible': [('team_id', '=', False)]}"
                    domain="[('activity_team_ids', '=', team_id)]"
                />
                <field
                    name="team_id"
                    options="{'no_create': True, 'no_open': True}"
                    domain="['|', ('res_model_ids', '=', False), ('res_model_ids', '=', res_model_id)]"
                />
            </field>
        </field>
    </record>

    <record id="mail_activity_view_tree" model="ir.ui.view">
        <field name="name">mail.activity.view.tree</field>
        <field name="model">mail.activity</field>
        <field name="inherit_id" ref="mail.mail_activity_view_tree" />
        <field name="arch" type="xml">
            <field name="date_deadline" position="after">
                <field name="team_id" />
            </field>
        </field>
    </record>

    <record id="mail_activity_view_form_board" model="ir.ui.view">
        <field name="name">mail.activity.view.form</field>
        <field name="model">mail.activity</field>
        <field
            name="inherit_id"
            ref="mail_activity_board.mail_activity_view_form_board"
        />
        <field name="arch" type="xml">
            <field name="user_id" position="attributes">
                <attribute
                    name="attrs"
                >{'invisible': [('team_id', '=', False)]}</attribute>
            </field>
            <field name="user_id" position="after">
                <field
                    name="user_id"
                    attrs="{'invisible': [('team_id', '!=', False)]}"
                    domain="[('activity_team_ids', '=', team_id)]"
                />
                <field
                    name="team_id"
                    domain="['|', ('res_model_ids', '=', False), ('res_model_ids', '=', res_model_id)]"
                />
            </field>
        </field>
    </record>

     <record id="mail_activity_view_kanban" model="ir.ui.view">
         <field name="name">mail.activity.boards.view.kanban</field>
         <field name="model">mail.activity</field>
         <field name="inherit_id" ref="mail_activity_board.mail_activity_view_kanban" />
         <field name="arch" type="xml">
             <field name="user_id" position="after">
                 <field name="team_id" />
             </field>
             <xpath expr="//div[hasclass('oe_kanban_content')]" position="inside">
                 <br />
                 <div>
                     Team: <field name="team_id" />
                 </div>
             </xpath>
         </field>
    </record>

        <!-- SEARCH VIEW -->
    <record id="mail_activity_view_search" model="ir.ui.view">
        <field name="name">mail.activity.boards.view.search</field>
        <field name="model">mail.activity</field>
        <field name="inherit_id" ref="mail_activity_board.mail_activity_view_search" />
        <field name="priority" eval="2" />
        <field name="arch" type="xml">
            <xpath expr='//field[@name="user_id"]' position='before'>
                <field name="team_id" />
            </xpath>
            <xpath expr='//filter[@name="activities_6_month"]' position='after'>
                <filter
                    name="my_team_activities"
                    string="My Team Activities"
                    domain="[('team_id.member_ids', '=', uid)]"
                />
            </xpath>
            <group position='inside'>
                <filter name='team' string="Team" context="{'group_by': 'team_id'}" />
            </group>
        </field>

    </record>
</odoo>