I have the same problem and I think that the opponent is cheating or boosting
That is absolutely not what is happening so stop flooding their system with false reports because you don't like dying.
This is because the CoD franchise has always had notoriously poor netcode that introduces a ton of latency between what's happening on your machine, your enemy's machine, and how both of them are communicating between the server. What you are seeing on your screen is not the literal position of where your enemy is, it is where your enemy was a fraction of a second ago. Because when he takes a step around a corner his machine has to communicate that data to the server, and then the server communicate it to you, and by the time you see it he's taken another step. And by the time you press ADS start firing "first", he's already started firing at you but the time delay between communicating between machines and the server make it look like you shot first. This also affects the accuracy of your shots as well because you might think you were hitting the very edge of his head but the server says nuh-uh he wasn't actually standing there so the bullet whizzes past and you die.
This is why you always feel like you're dying behind a wall even though you thought you got into cover. It's because according to the server and this fancy game of telephone it's playing between your machine and your enemy's machine, you were not yet in cover when you were shot even though on your screen it looked like you were. So that extra few frames that it is delayed allowed your opponent to land a few extra shots to kill you before the server says you got into cover.
This changes from game-to-game depending on your connection to the game server and whatever location your enemies are playing from. I had games when I was leveling the Kar/AMR where I felt like a god and literally every quickscope where I felt like I was on target was a hit/kill. Then the literal next game I feel like 2/3 of the shots I take, even though they felt on target when I shot them, the majority of them are missing. And that just has to do with those fractions of seconds where enemies are moving according to the server being delayed in telling my machine their locations as well as relaying the fact that I'm shooting at them.
This has been a CoD problem for over a decade ever since they introduced their godawful lag compensation. Normally when a player with slow connection reacts, his actions are delayed getting communicated to you, just as your actions are delayed getting communicated to him. This made them easier to kill because, when you peek him and start firing, if his connection was slow enough he might not even see you peek before he dies. Your machine communicated to the server that you peeked, the server communicated to you the enemy location while also sending communication to your enemy that you peeked, your machine communicates that you start firing and kill him, all before his machine even receives communication from the server that you came around the corner.
This creates a situation where the player with the bad connection cannot properly enjoy the game. So instead of just being satisfied with the notion that you need a competent internet connection to play online games, certain games like CoD decide to introduce higher lag compensation to "compensate" for those slow connections. To be clear, I believe just about every game now has lag compensation to a degree - some just have it more than others. CoD is very guilty in this case, as their M.O. has always been to appeal to as many gamers as possible, even the ones who still play over dialup.
Lag compensation allows the server to essentially rewind time to see where your enemy was when you peek and start shooting at him, to "compensate" for his bad connection and to try and "level the playing field" between your good connection and his shitty one. So back to our scenario above, you peek first and your machine communicates that to the server. However now when it communicates your location to your enemy and he reacts and fires back, even though you've already killed him on your end, the server has rewound time and said "no wait", technically the other player reacted faster than you did and killed you, his machine was just really delayed. That logic is fine in a vacuum, but it breaks down for a couple reasons. First it means when you "lost" you were fighting an enemy that wasn't even reacting to you peeking, because his connection was delayed. Second it means the player with the slow connection got to react to you in real time and the server rewound time to put him on a level playing field. So in essence, bad lag compensation reversed the situation from the player with the bad connection having a bad time, to the player with the good connection having a bad time.
Bad lag compensation punishes good connections by essentially reporting false information to you, because while it's rewinding time for your enemy and letting him react in real time, you are not getting the same experience any longer. This is why in the early days of Pubg, players were intentionally playing out of their region because it made their connection worse, which made the game easier. That is how stupid lag compensation is. Instead of saying "too bad you can't enjoy playing this game because you won't pay for decent internet" CoD says "no we will hamper the experience of every other player in order for you to enjoy this game as well". This would be like if Netflix said "oh we don't care that you pay for gig internet so you can stream 4K, little Johnny over here is on dialup so we're going to reroute your bandwidth to improve his experience and we'll just cap everyone at 1080p".
Here is an example of lag compensation. The red is the actual location of the enemy, the blue hitbox is where the server has rewound time to compensate for a poor connection. So if you were to shoot at his red front leg, the bullet would miss because according to the lag compensation of the server, his front leg is actually in the blue location. This is how what I described above happens. When I feel like I'm sniping someone in the head but it misses, sure sometimes I just missed. But other times it's because there was a fraction of a second delay between what the server is saying happened vs what physically happened on my screen, so a bullet that might've hit the edge of the hitbox on my screen and should've been a headshot, now misses completely because the server said so.