A 14.4 MB RAR archive labelled simply as Xiaomi M3, with no indication of what documents or files it holds. The model naming is ambiguous, as several Xiaomi and Redmi or Poco devices have carried M3 in their names, so verify which handset it actually refers to by examining the files and comparing board markings with your unit. Packs of this kind usually gather schematics, boardview data or firmware used for diagnosing power faults, shorts and component placement. Inspect the contents carefully before using them for a repair.
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 @esquemaseletricos. 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.