I am new and only 600+, as soon as I capture Queen opponent, 90% of the player quit, it is very frustrating and very disrespectful.
No it's not more the opposit. It's disrespectfull to continue! Don't make a foul of the game or yourself. Do not insult your opponent by not quiting for the idea maybee he make a mistake to.
You lost a queen and have nothhing in return ==> resign the game and play a new one. You can analise the game if you want. If you want ask the opponent to play again. In real life games the same but you can ask can we continue for study reassens. I think only 1% of real life games are played till checkmate. on toplevel 0.0%
For endgame practice, see under Puzzles, "Practice (Drills)" and "Endgames".
Terrific learning tools.