First of all it is important to define the product reservation configuration

If you want to work with Current demands, MTO (or replenish on order) can be a good solution, but limited, because if you need for example 3 units and you already have 2 in stock, the MTO route will generate the need for 3.
Better would be to use Replenishment (inventory->operations->replenishment) and create Reordering rules with quantities for example minimum 0 and maximum 0 for your products and components and trigger these rules automatically or manually according to your preference.

For Forecasted long/mid term demands could be interesting to implement MPS (available only for the enterprise version) you can find more info in the documentatrion: https://www.odoo.com/documentation/saas-15.2/applications/inventory_and_mrp/manufacturing/management/use_mps.html

On the MTO route (assuming you have this route, else your defined route), modify the rule (Stock to production), change 'supply method' to Take From Stock, if unavailable, Trigger Another rule

To access the route & associated rules, you would require to enable multi-step routes in inventory/ settings