Although Odoo does not officially support a “shared warehouse” setup due to legal and accounting implications, it is still possible to operate transactions through a common physical warehouse by configuring routes properly.

Here is a practical and stable approach that we have implemented for a similar multi-company scenario:

Company 1: Test1 Info

Warehouse: Test1 Info

Company 2: Test Info

Warehouse: Test Info

Configuration done through company "Test Info"

Configure Routes: Buy and MTO and configure the supplier warehouse as "Test1 Info", warehouses as "Test1 Info",

Create a product and enabled routes MTO and buy (for which we have done the configuration) and select the vendor in purchase tab

Create SO and select the company as "Test1 Info" in other info tab and confirm it, PO will be generated and receipt will be triggered, select the operation type which belongs to another company, 

Automatically location of another company will be set, which obviously update the warehouse of another company. Through this process we can handle single warehouse through multiple companies for transactions

Based on Odoo’s default configuration:

• Direct transfers between different companies are not allowed; this is only supported for inter-company branches.
• Transfers can be done only between internal locations.

For example:

If you have Company A and Company B, you can create an internal location and leave the Company field empty.

By keeping the location unassigned to any company, both Company A and Company B can use this location for transfers.