Why does Fritz say this is a blunder?

Here I played Qf6 but Fritz considers this to be an outright blunder and gives instead 31...Rxf2 32.Kxf2 Ra2+ 33.Bd2 Qf6 but doesn't elaborate further. I don't understand why 31...Qf6 is such a blunder. Any ideas anyone?

I don't have Fritz but Stockfish shows that Rxf2 is winning for black (-+), where Qf6 just gives a clear advantage to black (-/+). There is the difference in scoring of approximately 3 pawns, so it could be considered a blunder on those grounds, however, black still is doing OK.

After the line Fritz gave, black is threatening to infiltrate white's position. One way to try and understand what the engine is looking at is to play out some of the lines and see why other lines might be worse.

In that line, 34. Rd1 is coming. Without that, say with Kg3 (or Qe3) then engine likes 34... Rxd2 35. Qxd2 Qxf3+, followed by taking the pawn on g4. Black has a ton of pressure and will very likely win the h5 pawn too, creating passers on the king-side.

Some of the other lines the engine gives, end up attacking additional pawns. If the queens come off (with the rooks still on the board), then all the pawns on the 4th-rank become targets  since white can't protect them all.

Sorry cant be bothered setting it up but after Rxf2 Kxf2 Ra2+ Bd2 Qf6 Rd1 doesnt black have Qf4?  Intention would be Nxf3.

Tiger nxf3 was at the end of the chain, bro.  After 34 Rd1 Qf4 35 white move and 35...black x on f3.  I didnt say much but clearly it wasnt just nxf3.

Tiger, I have been playing chess for 36 years and yes it is part of chess talk, as you put it.  I think the context would have made it self-evident also.  Back out while you can.

Have you ever spoken to anyone?  They say takes.  x means takes, its standard terminology.  I think you need to learn the basics, lil dude.  You are sidetracking though from the analytic point, so I suggest you deal with the chess and grow up later.  The line I gave shows it is crushing, which is why Fritz gave the given move as a blunder.  The only reason I mentioned length of time was your own sentence "not part of chess talk" - a phrase I have never heard in "chess talk".

Both moves win, but swapping rooks first is much simpler.

I am second, that is exactly the line I was talking about.  From your diagram 5)...Nxf3 instead of 5)...Rc2.  Just plain wins.