How do you prevent mouse slips?

As far as I remember the older version 2 had not such a problem. Therefore there I could play minute games because more fluently the interaction with the application. So to me it looks the problem is not on my side.

Is there something like a move confirmation option in the settings?
I don't believe there is such an option, however if you're afraid you might drop a piece on an unintended square while holding it, you can consider making moves by clicking the piece and then the square, rather than dragging the piece somewhere.

On another note - recently I had an opponent agree to a draw after I made a most obvious mouse slip in the opening
I asked for a draw - which was very kindly granted. The opponent was from India.
I played game two as white - fully intending to repeat the line (without the King move) on game three. My opponent played some 15 or 18 very reasonable moves - and then disconnected in an equal and rich position - and simply lost!
I wrote him a note, that he can have his rating points back any time simply by asking - but haven't heard from him since.
So now I have a 2040 blitz rating - with a nine-point (or so) debt.
I'll be happy to accept those nine points
(jk)

When you are dragging a piece and want to retract always drop the piece on top of the opponent's king, capturing the king is always an illegal move so it"s a sure way to go back safely.

... Kf8 instead of 0-0 must be the worst, I always point and click now and only drag pawns, Knights and Kings but never Queens, Bishops and Rooks.

I also has to lost because of this on many occasions