I tried to build a signed release apk using Android Studio and I ended up with the error
"Transform's input file does not exist: /Users/thiru/Documents/al/build/app/intermediates/flutter/debug/libs.jar"
This is a known issue and solving this error is very simple.
If you look at the path in the error, it should either end with debug/libs.jar or profile/libs.jar. Based on the error you have to build the debug/profile apk before building the release apk.
If your error says debug/libs.jar, build –debug then –release.
If your error says profile/libs.jar, build –profile then –release.