To save space, repackers sometimes remove:

: Some antivirus software may flag legitimate game files as false positives, but with compressed unofficial versions, it is difficult to distinguish a false positive from a real threat. 2. Performance and Installation Issues Extreme Install Times

Repack may have stripped non-English audio. Fix: Download the English sound pack separately or change your Windows audio format to 24-bit, 48000 Hz.

A "highly compressed" version of a game is a repack where the installation files have been squeezed using advanced compression algorithms (like FreeArc or LZMA) to reduce the file size significantly.