This Application and Security, and Setup event logs in my update of Windows 10 to 21H2 last night.
The event service is running fine, and new log entries were created since the update.
Can you check this folder? Windows.old\windows\system32\config
The C:\windows.old folder does not exist on this system.
This article [ https://learn.microsoft.com/en-us/answers/questions/383487/events-log-are-deleted-by-kb4562830-update.html ] mentions the event log can be cleared by a Feature update.
Is this the intended behaviour, or an anomaly?
This is definitely not ideal behaviour from a sysadmin & system security perspective!