Microsoft removed a Windows 10, version 2004 compatibility hold blocking devices with certain WWAN LTE modems from upgrading to the latest Windows version. A fix for the issue was made available with the release of the Windows 10 2004 KB4577063 non-security preview cumulative update. Microsoft advises customers not to manually update if the May 2020 Update is blocked to avoid experiencing issues that might potentially make their Windows 10 devices unusable. You can still force upgrade your device to Windows 10 with the Media Creation Tool or Windows 10 Upgrade Assistant.
Source: https://www.bleepingcomputer.com/news/microsoft/microsoft-removed-another-windows-10-2004-safeguard-hold/