[2021] Where is the reserve?

When you mean here?

The update of the Commander Skills also aimed at cleaning up the organization of commanders themselves and optimizing the Commanders UI.

The short answer is those commanders for ship lines you currently don't have (if you sold one of your Commonwealth ships) then you will not be able to assign them to a ship for specialization/training.

The commanders haven't been removed, but will not be visible until a ship is available for them to be assigned to.

#anchorsaweigh