Rostyslav Are you using Manufacturing Orders, If the production process for Product A is more complex and requires specific manufacturing steps, you can use manufacturing orders instead of a Bill of Materials.
Create Product "A" Go to Odoo's Inventory app. Create Product "A" as a stockable product.
Create Product "B" and Product C Create Product "B" and Product "C" as stockable products if they don't already exist.
Configure Routes As in Option 1, configure routes for Product A, Product B, and Product C to specify the desired warehouse movements.
Create Manufacturing Orders When you create a sales order for Product "B", manually create a manufacturing order for Product "A".
In the manufacturing order, specify the quantity of Product A to produce. As the manufacturing process progresses, Product A's stock will decrease, and Product C's stock will increase. This option is more suitable if you have a complex production process with multiple manufacturing steps for Product A.