Which part of the game should a beginner spend most time studying?

Opening, midgame or endgame?

I'm having this discussion with a couple of people and each one of us has a different answer. One says midgame and endgame are far more important to study than openings while another believes endgames are the most important. I said openings would be the best to learn first because your response to certain black openings will affect your positions midgame. Without knowledge of how to properly respond to whites opening you'll find yourself in a bind early and playing from behind.
I look at many of my games as white on my main profile and notice difference in win percentage based on blacks opening.

endgame first. easiest to understand because few pieces.

Students in school also start with 2 + 1 and not 16 + 16.

endgame doesnt necessarily mean you learn the typical endgames. It can mean that you first look at mates with not more than lets say seven pieces on board. This for example is the approach of the book 'Bobby Fischer teaches chess'. he starts with the mates, with just few pieces. Sounds like a good idea to me if the first the beginner learns is how to mate.

You're rated over 800 points higher than beginners, so what is important in your games is not necessarily very relevant to beginners.
Really, beginners need to study all three to some extent:
Opening---beginners should focus on objectives and strategies (control the centre, develop all minor pieces to good squares, keep the king safe, avoid time-wasting moves and premature attacks) rather than studying reams of lines and variations.
Middlegame---beginners should learn what skewers, pins, forks,...... are and do puzzles to learn to find them.
Endgames---beginners should learn how to mate with a queen, and with a rook, how to stop a pawn with the king, the rule of the square, and also basic concepts like king activity.

Really, the vast majority of beginner games are decided by tactics in the middlegame, and concepts like "a bind" (irrelevant at beginner level) can be learned when they gain some experience.
See this thread:
lichess.org/forum/general-chess-discussion/frustrating-losing-streak

Simple observation shows that beginners should concentrate on the art of not hanging pieces.

#4 this isn't my main profile. I started playing mostly rapid games with a peak of 2044 on my main profile. Currently 1838. I need to stop playing bullet and blitz and get back to rapid

So you are rated higher on your main profile?
That means concepts important at your level are even less relevant to beginner play then I thought before.
Really, things like positional binds and minority attacks are not very important when every third move drops a piece.

I know right!

A beginner has to start with the opening.

Endgame for sure.
First 3 men endgames, then 4 men endgames, then 5 men, then 6 men. It is exact knowledge, certain to be true. It is useful in its own right and it teached you how to co-ordinate pieces. It teaches you what to aim for and what to avoid in the middle game and in the opening.