Computer annotations these days commonly use
?! to indicate moves which are noticeably worse than the best move, but not bad enough to warrant a
??. There's not necessarily any merit to the move, as there would have been in the old meaning to the annotation.
The program I use to auto-annotate my games uses a threshold of 3 for
??, 1.5 for
?, and 0.5 for
?!. Other programs may use other thresholds, but the idea is the same.
The program I use will not use these annotations for the losing side once they're already losing by a sufficient amount. Apparently lichess will still use
?! but not
?? annotations, in this situation. I believe this makes some sense, as the "best" move in a hopeless situation is not necessarily the move which postpones the mate for the longest. But the computer isn't that great at finding "merit" in objectively losing moves.
Can there be merit in a move that allows a forced mate? There wasn't in your case, but it can happen. I remember one game from my high school days where I was hopelessly losing (down a piece, and my opponent was about to promote) but I noticed I had a draw possibility if I could get my queen to a certain square. The catch was, it would take two moves to get there, and my opponent had a forced mate in 2 once I made the first queen move. I went for it anyway, he didn't notice the mate or my draw threat, and I stole a draw. Playing the "best" moves at that point would have been a certain loss.
I'm not quite sure why I still have the notation sheet for that game, but I do, so here's how that one ended:
[FEN "1Q6/1Npqkp1p/2p5/P3p3/2P1p3/1P5P/5PPK/8 w - - 0 36"]
1.a6 Qf5?! 2.Qxc7+?? (2.Qd8+ Ke6 3.Nc5#) Kf8 3.a7?? Qf4+ 1/2-1/2