The message appears to be saying that the Finder could not find one or more files – and as far as I know, Apple does not provide any more information about it than that.
I don't know if the bug still exists in macOS 13.3 (Ventura) – the version of macOS that your tag line says you're running – but in the old days, the Finder sometimes had problems copying very large numbers of files at a time. The typical symptom of this was that you got (you guessed it), error code -43.
The workaround was to use a clone backup utility like Carbon Copy Cloner or SuperDuper! whenever you had a really large number of files to copy. It shouldn't have been necessary to do this; copying files from one place to another is, after all, a pretty core function of the Finder! But in practice, that was the fix back then.