Hiding field selection's option in FormView
Usages :
change attributes if existing field
<xpath expr="//field[@name='existing_fields']" position="attributes">
<attribute name="widget">custom_selection</attribute>
</xpath>
Or add it as widget if new field
<field name="new_field" widget="custom_selection"/>
Do not forget to add the file in web.assets_backend
<template id="assets_backend" inherit_id="web.assets_backend">
<xpath expr="//script[last()]" position="after">
<script type="text/javascript" src="/your_module/static/src/js/widget.js"/>
</xpath>
</template>
Tested on Odoo 13