Some Question

I am a good chess player like an intermediate But i play so well and my mistakes is so low (I barely get a blunder or mistake these days) But i have a problem which is the Time management and also the High level Endgame , If someone can help me i will appreciate it 

For time management, try practicing with shorter time controls to improve decision-making speed. For advanced endgames, consider studying positions and techniques like opposition, zugzwang, and pawn promotion.

bro if you play shorter time control, you can't play slowly when you're in a classical game.
so it doesn't help if you do that.
second, about that endgame, you're wrong too. he said :
 High level Endgame...and studding opposition, zugzwang, and pawn promotion is very fundamental.
by the way, it's my problem too. so i can't fix it to you till i fix it for myself!!! 

try playing in 3 minute 2 second increment per move

im rubbish cant get to 800, maybe because im old, and i only play blitz 5 min,

OP I thinkk you should still play rapid chess as no offence ut I dn't think you haveno blunders and barely any mistakes based off your rating

Bro I personally feel like less time controls allows you to think faster and quicker with great Accuracy .. Like playing blitz helped me to think quicker and calculate faster

Guys how do I get 2100 USCF and now I am 1678

Guys, I'm new to chess so i want to ask some tips to get better at chess.

Some question i want to ask :
- what is the best opening for beginner?
- how to reduce blunder and analyze the position?
- how do you guys learn chess? (from bot, coach, or youtube vids?)
That's all i want to ask, Thanks!

Thank you for the advice! I'm actually using king's gambit, king's gambit is my favorite opening if i play as white. But for black, i always struggle to find good opening. Do you have recommendation opening to play as black?

my rapid rating was 675 but it fell to 570 over a course of three days. i still bridged a 300 point gap to win the champion title, but i still want to get my rapid rating back up and even to 700. what would you say i do

15 | 10

-Opening: learn the basic principles and adhere to them. I'd advise centre game, ponziani or danish gambit as white and Petroff defence, slav or 1 of the QGD variations (cambridge springs is fun with lots of traps) as black.
-Avoid blunders: don't really know. Just play a lot?
-Analyse position: after a game go over it slowly move by move (WITHOUT AN ENGINE), try to improve your play, find missed tactics/defences, discuss the moves with your opponent if possible or else a friend. When finished switch on the engine to show things you still missed.
- I learned from books (I'm old) playing through GM games. Doing lots of tactics puzzles. Silman's endgame book. And recently some youtube vids, ChessCoachAndras on youtube highly recommended!

https://www.chessable.com/basic-endgames/course/6371/

I'm guessing you take too much time and play accurately rather than too little and inaccurately. One way to get faster is to get better at calculating. The best players can play fast because they're very fast and accurate with their calculations, and they trust their calculations without having to double triple quadruple check their lines. Of course, your rating might go up then too, leaving you with the same problem.

For calculation speed, puzzle rush and puzzle battle might be useful.