The Build service should automatically minimize app size through the limiting/removal of features known to not be used by the app being built.
For example, if an app doesn't require any data connections, then there shouldn't be any permissions, functions, modules, or libraries that have anything to do with data connections.
My current app (which is fairly simple) currently clocks in at 46MB. This is roughly the same size as the Drizly, Google Fi, and Google Lens apps, which are far more complex and feature-rich than what I have built and deployed.