I try to add a custom Boolean field to model res.users and put it on the User Preferences Form. The problem is that normal users have no rights to change this field on saving. Any idea howto deal with this?

Sorry, you are not allowed to modify this document. Only users with the following access level are currently allowed to do that:
- Administration/Access Rights
(Document model: res.users) 

from odoo import models, fields
class ResUsers(models.Model):
    _inherit = 'res.users'
    sidebar_visible = fields.Boolean("Show App Sidebar", default=True)

<?xml version="1.0" encoding="utf-8" ?>
<odoo>
    <record id="res_users_preferences" model="ir.ui.view">
        <field name="name">res.users.preferences</field>
        <field name="model">res.users</field>
        <field name="inherit_id" ref="base.view_users_form_simple_modif" />
        <field name="arch" type="xml">
            <xpath expr="//group[last()]" position="after">
                <group name="App Sidebar">
                    <field name="sidebar_visible" readonly="0"/>
                </group>
            </xpath>
        </field>
    </record>
</odoo>