petri[.]com/how-to-enable-reserved-storage-using-dism-or-powershell-in-windows-10-version-2004
Windows 10 has a feature setting aside some hard disk storage space for updates and other Windows use. If you install Win10 fresh, it's enabled. If you upgrade a copy of Win10 where it is not enabled, it will remain disabled. This short article gives the CLI commands to turn it on/off using DISM, & the commands to use with Powershell if you prefer that.