https://www.bleepingcomputer.com/news/microsoft/microsoft-removed-another-windows-10-2004-safeguard-hold/

Microsoft removed a Windows 10, version 2004 compatibility hold blocking devices with certain WWAN LTE modems from upgrading to the latest Windows version.

Safeguard holds (also known as compatibility holds) are added by Microsoft based on known issues and diagnostic data to delay Windows upgrades on affected devices and to protect the end-users' smooth experience.