Yes, you can create a bill of materials (BOM) that includes the same finished product as a component and run a manufacturing order for it in Odoo Enterprise v15. To do this, you would first create a BOM for the finished product and specify the quantity of the finished product that you want to use as a component in the BOM. Then, you can create a manufacturing order for the finished product and specify the quantity that you want to produce. This will deduct the specified quantity of the finished product from your stock and produce the updated or dismantled finished product. Keep in mind that this may not be the most efficient way to handle this type of situation, and it's always a good idea to carefully consider your manufacturing processes and inventory management strategies to ensure that you are using the best approach for your business.

Yes thats correct, you can only unbuild what you built as @Lars Aam has highlighted in his response. 
>>Dismantle is standard (for something that has been manufacttured)<<

Odoo would only create components (&Qty) that is were used in the specific MO (BOM) that you choose to unbuild.

In your case, you need to use the product that you wish to dismantle as the component in BOM and register the manufactured products and by-products (outputs).

Hi thanks for thoughts. But what if a manufacturing company Buy products, and sell in parts (dismantling). Using unbuild function we can dismantle into given quantities in the BOM. But through out the unbuild process we cannot change the quantities like in output in manufacturing order.

Any suggestion in that case

You cannot have the same product manufactured as you have as component. So you would need to different products. Which also make sense  - you change the product in the process, so It needs a new identity.  Variants might be an option.

Dismantle is standard (for something that has been manufacttured). Manifacturing app. Operations->Unbuild.