Thank Andre for your very helpful suggestion. Below full solution:

I replace:

 <field name="route_new_ids" widget="many2many" domain="[('product_id','=',id)]"/>

by:

 <field name="route_new_ids" domain="[('product_id','=',id)]" context="{'from_product': True}">
<tree create="false" delete="false">
  <field name="sequence" widget="handle"/>
  <field name="route_id"/>
</tree>
</field>       

context="{'from_product': True}" allows to disable, after click on list position, in form view, editions other fields than sequence

options="{'no_create_edit': True}"

specify this in your many2many field,

<field name="your_field" widget="many2many_tags" options="{'no_create_edit': True}"/>