Welcome!

• activate the developer mode and go to settings->technical-> automation rules (in Odoo enterprise it can also be done opening studio from a inventory receipt)
• create the following automation:

Code:

# The action works for related purchases generated by MTO or reordering rules

pickings = records or record

for pick in pickings:
  all_purchases = pick.mapped("move_ids.purchase_line_id.order_id")
  for purchase in all_purchases:
    # Parse origin string to find related sale orders
    if not purchase.origin:
      continue
    all_origins = purchase.origin.replace(", ", " ").replace(" - ", " ").split()
    orders = env["sale.order"].search([("name", "in", all_origins)])
    for order in orders:
      order.activity_schedule(act_type_xmlid="mail.mail_activity_data_todo", summary="Receipt from related purchase %s" % purchase.name, user_id=order.user_id.id)