APKMirror Installer is a helpful app that allows users to install different types of app files, including .apkm, .xapk, and .apks app bundle files, as well as regular APK files. It also has a feature that helps users understand why an APK installation has failed. The app explains the concept of split APKs, which are a result of the new dynamic app delivery format called App Bundles. APKMirror Installer solves the problem of missing resources by allowing users to select only the splits they want to install.

.apkm files are a solution developed by APKMirror to adapt to the changes in the split APK format. Each .apkm file is comprised of a base APK and a number of split APKs. Users can select only the splits they want to install to save space on their device. The app is ad-supported, but there are subscription options to go ad-free and unlock additional features.

For Xiaomi/Redmi/Poco MIUI users who face issues with installing split APKs, there is a workaround. They can disable MIUI optimizations in developer settings. Other issues/bugs can be reported to the Github bug tracker. It is important to note that this app is a file manager utility and does not have any direct app store features.

Overall, APKMirror Installer is a useful app for those who want to install different types of app files and understand the concept of split APKs. It offers a solution to the problem of missing resources and has subscription options to go ad-free and unlock additional features.