Yup! It's a major step in building any Java application. Things like stripping symbol names, removing unused APIs, and processing non-java assets like images. For Android applications Gradle handles this by invoking some Android specific utilities alongside the java ones, but there's tons of build tools out there for Java that handle doing these things for everything from Blu-Rays to web apps.
Unfortunately you can't treeshake a language that supports reflections. So it's not like a C++ program where unused parts get dropped.
You can manually remove dependencies or.. I think in the Android world you specify what classes can be reflected on and then strip unused code with Proguard (though I could never get it working with Clojure)
Would love to be corrected if I got any of it wrong
I'm afraid you did get it wrong - it's very standard to do that on all Android apps. The part that you missed is that reflection is rarely used in production apps (partially because for a long time, reflection was VERY expensive on Dalvik/ART runtimes) and can be easily handled by configuration for minifier/optimizer to explicitly keep code.
Even C++ you mention does that - you have explicit __attribute__ calls to avoid linker from dropping code you want to keep for reflection purposes.
Yes, it's enabled by default even in tutorial Android apps - Proguard was the tool used in olden days and has now been replaced by Google developed R8 optimizer/minifier.