Beginner Frustration
Thats kind of rude that they quit. I am new as well and I find I enjoy playing a few slow daily games so I can focus more and learn.

Hi! I noticed players are much more likely to quit if the game isn't ranked. Make sure to change settings and see if it helps.

Just block those players so that you won't get paired again and move on. Once you improve and get a higher rating you will face more serious players who show more respect for the game and their opponents.

I am furious! Several times I solve a chess puzzle by a slight variation which is equally valid and it's considered a mistake. For example, I have a choice of moving a queen or a rook first and then the other piece to end in checkmate. Moving one of these first is considered valid and the other is judged a mistake. I just tried to solve a puzzle which had me stymied and the solution involved moving a pawn diagonally to an unoccupied square!? There should be a way to inform the powers that be when a mistake like moving a pawn diagonally is shown as a solution!!!
There are rules against quitting that much, these players will get restricted by chess.com if they keep aborting their games early. I think this phenomenon doesn't happen as much after a certain Elo rating, so just keep playing and take the free points if they quit.

I am furious! Several times I solve a chess puzzle by a slight variation which is equally valid and it's considered a mistake. For example, I have a choice of moving a queen or a rook first and then the other piece to end in checkmate. Moving one of these first is considered valid and the other is judged a mistake. I just tried to solve a puzzle which had me stymied and the solution involved moving a pawn diagonally to an unoccupied square!? There should be a way to inform the powers that be when a mistake like moving a pawn diagonally is shown as a solution!!!
There's an analysis button that can show you the differences. More often than not it might be something like:
variation A leads to checkmate
variation B your opponent sacs their queen and plays on
therefore variation A is better.
you don't need a membership to do the self-analysis, I think.

Couldn’t find it looking through your puzzle history but are you sure it wasn’t an en passant capture? (If the last move before the puzzle was a pawn advance, you might have missed that this was a legal option.)

I am furious! Several times I solve a chess puzzle by a slight variation which is equally valid and it's considered a mistake. For example, I have a choice of moving a queen or a rook first and then the other piece to end in checkmate. Moving one of these first is considered valid and the other is judged a mistake. I just tried to solve a puzzle which had me stymied and the solution involved moving a pawn diagonally to an unoccupied square!? There should be a way to inform the powers that be when a mistake like moving a pawn diagonally is shown as a solution!!!
There's an analysis button that can show you the differences. More often than not it might be something like:
variation A leads to checkmate
variation B your opponent sacs their queen and plays on
therefore variation A is better.
you don't need a membership to do the self-analysis, I think.
I can confirm it isn't needed, only to make a game report.