Once the Microsoft Store is installed, you can use it to launch sideloaded apps, but I haven’t been able to get installation directly from the Microsoft Store to work as of yet.
The process involves downloading the desired app from this site: https://store.rg-adguard.net and then double-clicking it to install it (using the App Installer installed by the script). After that, you can open the Microsoft Store to launch the app as normal. Note that developer mode or the “sideload apps” mode must be enabled for this to work.
Encrypted Microsoft Store apps (.eappx) are more difficult. You would need to install the app on another computer, run UWPDumper (https://github.com/Wunkolo/UWPDumper), and then repackage and sign the app and send it to the Server 2016 instance, where it can be installed by double-clicking it. It can then be launched from the Microsoft Store. I used this process to install Hellblade: Senua’s Sacrifice for Xbox Game Pass, but the process was very time-consuming.
Unencrypted apps can be quickly installed by users, but installing encrypted apps takes more effort. It would be more accessible, however, if the process was partly automated.