By default, Android SDK is expected under ~/android/sdk. It is possible to adapt this path in docker-compose.yml. But it may also be specified in your local.properties!
The following command should build (if required) and start a shell session inside the container:
docker-compose --compatibility run --rm default
From there, Gradle and Fastlane should work as expected:
./gradlew tasks fastlane lanes
Most importantly, Fastlane or the whole bundle can be updated:
bundle update fastlane bundle update