Hi,

In Odoo 19 this behavior is expected, as the route selected on the sales order line is not treated as a strict override. When multiple routes are available for a product, Odoo automatically evaluates all applicable routes and applies the one with the highest priority based on stock availability and procurement rules, which is why an in-stock product may follow a Buy or internal route even if Dropship is selected. To achieve the desired behavior, you should ensure only one sales route is enabled on the product, adjust route priorities so the intended route (such as Dropship) has higher priority, use separate products for stock and dropship scenarios, or implement a custom procurement override to strictly respect the sales order line route.

Hope it helps

Do ensure the ‘Pull from Stock to Customer’ rule on your delivery route, has the supply method set to ‘take from stock, if unavailable trigger another rule’

It is also possible to set supply method to ‘take from stock’ and define replenishment route