My fertility charting app still works perfectly on older devices, but the current build targets an outdated SDK and refuses to install on phones running Android 10 and above. The goal is simple: update the codebase so it compiles cleanly in the latest stable Android Studio, installs without warnings on Android 10 → 16, and keeps every existing screen and feature exactly as they are today. What needs to happen • Raise the compile/target SDK level and migrate any deprecated APIs or support-library calls to AndroidX. • Update Gradle, dependencies and signing configs, ensuring 64-bit compliance and Play Store policy readiness. • Retain the present UI, workflows and data model—no new functionality or design overhaul is required. Performance optimisations are welcome so long as behaviour remains unchanged. Deliverables 1. Updated project source in a ZIP file. 2. Release-ready APK (and AAB) that loads flawlessly on physical devices and emulators from Android 10 upward. 3. A short change log describing every file or library touched, plus build instructions I can reproduce. Acceptance The build installs through the Play Console’s pre-launch report with zero critical issues, opens charts, registers data, and syncs exactly as the current version does on legacy phones. The code is predominantly Java with a touch of XML; feel free to introduce Kotlin only where it replaces deprecated calls cleanly.