web/web_widget_many2one_simple/views/assets.xml

<?xml version="1.0" encoding="utf-8" ?>
<odoo>
    <template
        id="assets_backend"
        name="Web Widget Many2One Simple Assets"
        inherit_id="web.assets_backend"
    >
        <xpath expr=".">
            <link
                rel="stylesheet"
                href="/web_widget_many2one_simple/static/src/css/many2one_simple.scss"
            />
            <script
                type="application/javascript"
                src="/web_widget_many2one_simple/static/src/js/many2one_simple_field.js"
            />
        </xpath>
    </template>
</odoo>