Boardview for the Quanta QT6A main board, the MB-C part of the name likely denoting the motherboard at revision C. The file is a 352 KB .brd readable in OpenBoardView, FlexBV and comparable programs. It maps every component and net, so a technician can click a rail, see all connected parts and pick convenient measurement points. Because QT6 boards come in A, B and UMA versions, verify the variant and revision printed on the PCB before trusting the layout, and use it with the QT6 schematic.
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 @pepeelectronica. Enginerys does not host this file.
How to open a .brd file
The most common boardview extension. Several unrelated formats share it, which is why one viewer opens a .brd and another refuses it.