Are you sure its not +5.44 ?

You are correct the 3rd move (Nf6+) is not correct, In fact its not legal.

An article about it :- https://en.chessbase.com/post/aphantasia-in-chess

Try the Queens gambit ?

I recommend you study "Silman's Complete Endgame Course From Beginner to Master"

The answer is not going to be to play more with time controls but playing long time controls and spending time (maybe years) thinking deeper in lots and lots of different positions until you can calculate well then you will be able to speed it up as you have a lot more knowledge of the positions you get into.