An archive of repair files for Apple hardware (board 820-3126). Shared as “Apple iMAC A1311 21.5 820-3126-A.rar” — a .rar file, 6.63 MB.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @IT_SERVICE_WORLD. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.
7-ZipWinRARThe Unarchiver (macOS)