If you are getting an "Unexpected end of archive" or "Checksum error" specifically pointing to part 11, the file is likely damaged.
Click the (next to "Play") -> Manage installation -> Verify / Repair . A.Plague.Tale.Requiem-GOG.part11.rar
: Open part11.rar in WinRAR, go to Tools , and select Repair archive . WinRAR will attempt to create a "fixed" version of that specific part. If you are getting an "Unexpected end of
To extract the game files, you cannot open just "part11.rar" on its own. You must have (e.g., part1 to partXX) in the same folder. go to Tools