Apk extractor from F-Droid doesn’t seem to work. App in question is Typewise Offline (android keyboard with hex-shaped keys).
EDIT: Probably worth a separate post at some point, but this is one of the few apps for which there is no open source equivalent, TTBOMK, and one of the few remaining proprietary apps that I rely on.
Even if you extracted the APK, apps can tell how they were installed and may refuse to work if it wasn’t via the Play Store.