Unlock Check is a native Android app (Kotlin, Jetpack Compose, Material 3) that shows when your phone was locked and unlocked. It reads Android's own usage events, so history from before you installed it shows up too. It keeps its own copy on the device so the history goes back further than Android keeps it. It has no internet permission.
./gradlew assembleDebug adb install -r app/build/outputs/apk/debug/app-debug.apk adb shell appops set ca.morristech.unlockcheck GET_USAGE_STATS allow # or grant in Settings › Usage access
Needs Android 9+ for lock events (minSdk 26). See the README in the source repository for details.