It's possible to make a small change to the XML (you can start it in Odoo Studio but this type of domain is not supported so you have to edit the XML for the extension view):

<data>
  <xpath expr="//field[@name='product_template_id']" position="attributes">
    <attribute name="domain">[('seller_ids.partner_id','=',parent.partner_id),('purchase_ok', '=', True)]</attribute>
  </xpath>
</data> 

Using Odoo Studio:

1. Create a new 'Many2many' field (related to 'product.product') on the Purchase Order model.

   * Name it like vendor_products.

   * Set it as computed, with a dependency on 'partner_id'.

   * In the compute method, search for products where the selected vendor ('partner_id') is listed in the product's vendor list ('seller_ids').

   * Mark this field as invisible on the form.

2. Add a domain to the product field in the Purchase Order Line model.

     [('id', 'in', parent.vendor_products)]

Let me know if you'd like a demo feel free to contact me via WhatsApp at 7538824350 or send me a DM.

Hi,

Please refer to the code:

from odoo import api, fields, models

class PurchaseOrderLine(models.Model):

    _inherit = "purchase.order.line"

    product_ids = fields.Many2many(

        'product.product',

        string="Allowed Products",

        compute="_compute_product_ids",

        store=False,

    )

    product_id = fields.Many2one(

        'product.product',

        string="Product",

        domain="[('id', 'in', product_ids)]",

    )

    @api.depends('order_id.partner_id')

    def _compute_product_ids(self):

        for line in self:

            if line.order_id.partner_id:

                products = self.env['product.product'].search([

                    ('purchase_ok', '=', True),

                    ('seller_ids.partner_id', '=', line.order_id.partner_id.id)

                ])

                line.product_ids = products

            else:

                line.product_ids = False

Hope it helps.