Reserved storage was introduced in Windows 10 1903, if you have a new installed devices it is enabled by default. If your device is upgraded to Windows 10 1903 it is disabled by default.

Reserved storage starts by reserving about 7 GB of hard disk space and the amount of space reserved will vary over time based on the device. To ensure the device can successfully update and that it runs its best.
As part of Storage Sense Windows will do cleanup on your drive to ensure that you have enough free space.

With Windows 10 2004 there is new DISM commands to mange it – that can be set by Intune from running a PowerShell script.

How to enable reversed storage from Intune:

Start Microsoft Endpoint Manager admin center : https://endpoint.microsoft.com

1. Select Devices
2. Select Windows
3. Select PowerShell scripts
4. Click Add

1. Enter Name : Enable ReservedStorage
2. Enter Descriptions: Script to test if ReservedStorage and enabled if it is disabled

Download Enabled-ReservedStorage.ps1 script from Github

Set Scope tags and assignments as you need in your organisation,
In my scenario I have deployed to a group called all devices – always start with a test group.

You can always track if your script is working on the log file: C:\ProgramData\Microsoft\IntuneManagementExtension\Logs\IntuneManagementExtension.log

If you want to disable reserved storage then use this script:
Download Disabled-ReservedStorage.ps1 script  from Github

Happy testing

Read more:

Managing reserved storage in Windows 10 environments
How reserved storage works in Windows 10