The ShowError() API they're talking about doesn't take a format string. It takes a resource ID which is an integer that's essentially an index in the resource table. So running the message compiler produces a C header that defines ERROR_BITLOCKER_PASSPHRASE_MINIMUM_TOO_LONG to an integer constant, and then ShowError(ERROR_BITLOCKER_PASSPHRASE_MINIMUM_TOO_LONG) looks up the string at that index in the resource table and displays it.

https://learn.microsoft.com/en-us/windows/win32/eventlog/mes...

(You'll note that that page mentions that FormatMessage() does support printf-style format specifiers in the string resource. That's why I'm saying that their ShowError() specifically is the one that doesn't.)