A Manufacturing Order in Odoo can only make one Product.*

A Bill of Materials in Odoo can describe the components for as many things as you want by using something we call Product Variants.

You can setup a Product with Product Variants such as:

You can then create a Bill of Materials such as:

A single Bill of Materials that applies each Component to one or more Variants. You can also manage a single Bill of Materials per Product Variant where necessary.

Automatic re-ordering rules can schedule Manufacturing Orders for you, as can any Sales Orders you enter or you can use the Master Procurement Scheduler to plan for a known demand at a time.

Each Product Variant demanded will trigger a Manufacturing Order that knows which components should be used during production:

A Manufacturing Order for a single Basic T-Shirt that has Odoo Purple and Large as the Product Variant Attributes.

You add T-Shirts you sell to Sales Orders like this:

You can also add them like this to Sales Orders AND Purchase Orders (when you buy apparel):

On e-Commerce, Product Variants look like this:

Examples:

More Information:

https://www.odoo.com/documentation/15.0/applications/websites/ecommerce/managing_products/variants.html

https://www.odoo.com/documentation/15.0/applications/inventory_and_mrp/manufacturing/management/bill_configuration.html

https://www.odoo.com/documentation/15.0/applications/inventory_and_mrp/purchase/products/reordering.html

https://www.odoo.com/documentation/15.0/applications/inventory_and_mrp/manufacturing/management/use_mps.html

Note: * technically it supports by-products but that's not relevant for you.