What does F/10 and F/11 in MLB stats mean?

F means Final, indicating the game is complete. Prior to completion, it will show an innings count ("Top 5" meaning the game is currently in the 5th inning, and the Away team is at bat, so the Top of the 5th).

F/# means that the game is Final, and that the game finished in a number of innings other than the normal length (in most cases, 9 innings, though the new doubleheader rule means some games only go 7 by default). The game might end earlier (if there is a rain situation that causes them to call the game as final, which they can after 5 innings if they choose to, as opposed to suspending it and completing it later) or end later (if the game is tied after 9 innings).

F/10 then means that the game is completed, and was completed after 10 innings of play, presumably due to a tie game in regulation (9 innings).