Odoo Views Error: No default view of type ' form' could be found

When I click on the button I should see a list. There should also be the ability to create a new record. But when I click on the button I get:

No default view of type ' form' could be found!

How to fix it?

If I go from the main menu, then there is no such problem

<?xml version="1.0" encoding="utf-8"?>
<odoo>
  <data>
    <act_window
      id="attach_pdf_action"
      name="Attach PDF"
      res_model="attach.pdf" />

    <menuitem
      id="attach_pdf_menu"
      name="Attach PDF"
      action="attach_pdf_action"
      parent=""
      sequence="5" />

    <record id="attach_pdf_view_form" model="ir.ui.view">
      <field name="name">Attach PDF Form</field>
      <field name="model">attach.pdf</field>
      <field name="arch" type="xml">
        <form>
          <group>
            <field name="product_id"/>
            <field name="product_attribute_value_id"/>
          </group>
          <group>
            <field name="file" widget="binary" filename="file_name" string="Binary"/>
          </group>
        </form>
      </field>
    </record>

    <record id="attach_pdf_view_tree" model="ir.ui.view">
      <field name="name">Attach PDF List</field>
      <field name="model">attach.pdf</field>
      <field name="arch" type="xml">
        <tree>
          <field name="product_id"/>
          <field name="product_attribute_value_id"/>
          <field name="file_name" readonly="1"/>
        </tree>
      </field>
    </record>

    <record id="attach_pdf_view_search" model="ir.ui.view">
      <field name="name">Attach PDF Search</field>
      <field name="model">attach.pdf</field>
      <field name="arch" type="xml">
        <search>
          <field name="product_id"/>
          <field name="product_attribute_value_id"/>
        </search>
      </field>
    </record>

    <record id="attach_file_wizard" model="ir.actions.act_window">
      <field name="name">Attach PDF</field>
      <field name="type">ir.actions.act_window</field>
      <field name="res_model">attach.pdf</field>
      <field name="view_type">form</field>
      <field name="view_mode">tree, form</field>
      <field name="domain" > [('product_id', '=', context.get('product_name'))]</field>
      <field name="view_id" ref="attach_pdf_view_tree"/>
      <field name="target">new</field>
    </record>
    <record id="view_form_product_attr_pdf" model="ir.ui.view">
      <field name="name">attach_pdf_attribute_product_product_template_only_form_view</field>
      <field name="model">product.template</field>
      <field name="inherit_id" ref="product.product_template_form_view"/>
      <field name="arch" type="xml">
        <xpath expr="//header/button[@name='121']" position="after">
          <button name="%(attach_pdf_attribute.attach_file_wizard)d" context="{'product_name': name}" string="Attach PDF" type="action" class="oe_highlight"/>
        </xpath>
      </field>
    </record>

  </data>
</odoo>

It seems you have given white space in "view_mode" values. No need to give space between values.

Try with following code:

<record id="attach_file_wizard" model="ir.actions.act_window">
  <field name="name">Attach PDF</field>
  <field name="type">ir.actions.act_window</field>
  <field name="res_model">attach.pdf</field>
  <field name="view_type">form</field>
  <field name="view_mode">tree,form</field>
  <field name="domain" > [('product_id', '=', context.get('product_name'))]</field>
  <field name="view_id" ref="attach_pdf_view_tree"/>
</record>

EDIT:

Remove <field name="target">new</field> line.

Documentation:

• Windows Actions

• view_mode

comma-separated list of view types as a string (/!\ No spaces /!). All of these types will be present in the generated views list (with at least a False view_id)