Hi,

Try this code

from odoo import models, fields, api

class StockPicking(models.Model):

    _inherit = 'stock.picking'

    amount_taxed = fields.Monetary(string="Amount Taxed", compute='_compute_amount_taxed', store=True)

    @api.depends('move_ids.product_id', 'move_ids.move_line_ids.move_line_tax_ids')

    def _compute_amount_taxed(self):

        for picking in self:

            taxed_amount = 0.0

            for move in picking.move_ids:

                for move_line in move.move_line_ids:

                    # Sum up the taxes for each move line

                    for tax in move_line.move_line_tax_ids:

                        taxed_amount += tax.amount

            picking.amount_taxed = taxed_amount

Hope it helps