Microsoft has acknowledged a new known issue causing forced restarts on Windows 10 20H2 devices due to the Local Security Authority Subsystem Service (LSASS) system process crashing. The known issue only affects those devices where local built-in accounts such as Administrator or Guest have been renamed. Microsoft has also applied a new update block to prevent impacted devices from being offered or installing Windows 10, version 2004 or Windows 10. Microsoft says that it will provide updated bundles and refreshed installation media within the next few weeks, as soon as a resolution is available.
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-20h2-lsass-crash-issue-causes-forced-reboots/