I recently picked up a 43 inch Samsung RU 7100 - an outstanding TV, and games look great on the PS4 Pro.
The HDMI port assigned to the PS4 Pro has Game Mode set to Auto. When I switch to that port, the TV automatically goes into Game Mode. When I start an HDR game, the TV displays the message "Game Mode Off" twice in quick succession and then "Game Mode On". So far, it hasn't done that in-game, just when I start an HDR game. It also repeats these messages when I exit the game back to the main PS4 dashboard.
Question: do you recommend setting Game Mode to "On" instead of "Auto"? Is there any downside to doing so? E.g., if I'm going to watch a Blu Ray or TV series on the PS4 instead of playing a game?