In mid-2018 at Google I/O, Google announced a new dynamic app delivery format called App Bundles. We highly recommend reading this AndroidPolice post as the illustrations will make the concept a lot easier to understand.
Otherwise, here is a quick explainer. Before app bundles, developers either created a single "fat" APK with all the libraries and resources in them or manually managed multiple APK variants (for example, arm64 320dpi, x86 320dpi, arm64 640dpi, etc.).
The new App Bundles allow developers to transfer the burden of dealing with variants to Google, which then splits the app release into multiple chunks - hence the term split APKs. Each release then consists of a base APK and one or more APK splits.
For example, a single release may now arrive as 5 files: base.apk + arm64.split.apk + 320dpi.split.apk + en-us.lang.split.apk + es-es.lang.split.apk.
Unfortunately, you can't install all these APK splits by just tapping them on your device - you can only install the base APK, which will then crash due to missing resources.
Long of the short of it is, these can't be installed just by clicking to download, since they are now bundled as apkm files, however this opens up the oppurtunity to do something similar to what happens with aptoide links where if a apkm version is found on apkmirror the version doesn't have to be decided since there should only be one download, so that file can be downloaded and extracted within apkgrabber and the correct version can be installed, as it should be knowable which architecture you are currently on.
Will probably require some work but if anyone's up for it i'm willing to test :D
From the apkmirror app description:
Long of the short of it is, these can't be installed just by clicking to download, since they are now bundled as apkm files, however this opens up the oppurtunity to do something similar to what happens with aptoide links where if a apkm version is found on apkmirror the version doesn't have to be decided since there should only be one download, so that file can be downloaded and extracted within apkgrabber and the correct version can be installed, as it should be knowable which architecture you are currently on.
Will probably require some work but if anyone's up for it i'm willing to test :D