In old days. in CRM and Dynamics 365 CE we were able to add sub components using our custom solution or a default solution however things in Power Apps are a bit different.
Below is a screenshot of adding a sub component for an entity or an other component or adding all components.
However in modern days in Power Apps you need to go to link
Then select your solution and open it
Once you are into solution, select entity where you need to add components and you will ass option to Add subcomponents.