TP.MS638.PC822 (also commonly listed as MS638 PC822).
A common repository for board-specific firmware. You can find entries for the TP.MS638.PC822 board here. Download MS638 PC822 3840x2160 Mitashi Ref65 part02 rar
Primarily found in Mitashi 65-inch 4K models (likely the "Ref65" mentioned in your query) and other brands like Polar or Asano. Resolution: 3840x2160 (Ultra HD/4K). Download MS638 PC822 3840x2160 Mitashi Ref65 part02 rar