Please stop cross posting.

Has the cause of death been given yet ?

I have not seen any of his online stuff but to die at such a young age and to have helped a lot of players, RIP

Chess may not be the game for you.

Why did you plug this into lichess ?

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.