Installing google play services from APKmirror by command line APKmirror provides many modern apps as split apk tar files. For example, if I want to install the android webview apk, I can download it from here, and un-tar the .apkm file to produce the following split apk:
├── APKM_installer.url
├── META-INF
├── base.apk
├── icon.png
├── info.json
├── split_config.en.apk
├── split_config.es.apk
├── split_config.fi.apk
├── split_config.fr.apk
├── split_config.iw.apk
├── split_config.ja.apk
├── split_config.pt.apk
├── split_config.ru.apk
├── split_config.sv.apk
├── split_config.th.apk
└── split_config.zh.apk

This split apk can be installed with:
adb install-multiple -r -g -t &lt;directory&gt;/*.apk

However, for APKmirror's google play services found here, when I untar I get this:
├── AndroidManifest.xml
├── META-INF
├── assets
├── build-data.properties
├── classes.dex
├── classes2.dex
├── classes3.dex
├── classes4.dex
├── classes5.dex
├── classes6.dex
├── classes7.dex
├── com
├── googledata
├── lib
├── org
├── res
├── resources.arsc
└── stamp-cert-sha256

This looks more like an .aab file, however it is missing the required BundleConfig.pb file.
What type of app format it this, and how can I turn it into a split apk that can be installed easily?
The answer is:

This is apk app format
I can install by just renaming the download from .apkm to .apk.

Thanks to Robert for pointing this out!