How do i improve mental endurance and concentration

how do i improve my concentration and mental endurance

That's a very good question. I think we have to watch nutrition , including fluid intake. Don't have a heavy meal before a game.Also sleep quality. Make sure other things in life like fitness are in place etc

I notice many good players have jobs that demand concentration and despite not working that hard at chess away from the board are pretty good when they sit down to play a game.

As mentioned, things like sleep deprivation and bad nutrition along with lack of exercise will all be major vices to any player.

Exercise the brain. Solve puzzles. any puzzles like croosword puzzles, sudoku, etc. and increase time gradually like jogging farther and longer.