The .rar archive contains the update files and typically includes a small executable (often a custom installer) to apply the patch.
The v4.2.0 update for Cozy Grove primarily focused on substantial quality-of-life improvements and preparatory work for premium content. Cozy.Grove.Update.v4.2.0-SiMPLEX.rar
Included a "speculative fix" to prevent save file corruption caused by accidental time traveling, as well as general memory improvements for low-end devices. Cozy.Grove.Update.v4.2.0-SiMPLEX.rar