There is a vast gulf of difference between "the information is available to me, I just do not care to examine it" (a perfectly cromulent choice for any given person) and "I will not let the information be available to you regardless of your preferences." The former is a player choosing to play in the way they find most pleasing. The latter is the DM unilaterally declaring that all players must play that way.
Again, I don't need to know a monster's statblock (though you'd better believe I feel quite strongly about that statblock not changing without a diegetic reason once it's entered play). I do need to know how attack rolls actually work, if I'm going to be making informed decisions. Me knowing how attack rolls and saving throws works is the IRL abstract representation of my character having combat experience and being able to reason about dangers they face. I may not know the enemy's AC, but knowing my own statistics and what I've seen of the enemy is, in fact, the rules-side analogy of my character having intuitions about their ability (or lack thereof) to achieve success on the battlefield. Leaving that totally oblivious is, in fact, less like actually doing a real person's reasoning.
A real, reasonable (not perfect, just reasonable) person does not behave as though they are totally ignorant of their own capabilities when sincerely trying to succeed. Knowing that you need a 9 or better to hit (say) chainmail armor actually is a representation of your character's awareness of their abilities. That mechanical element precisely corresponds to the thought, "I've taken on jerks in chain before, it's still risky but the odds are in my favor." Yes, obviously, as a player you can be much more precise with those odds than the character could be, but that's the simple price we pay for having rules in the first place.
It’s really about how cleverly you operate the rules. I would never tell players they need a 9 to hit. Or that they need a 12 to disarm the trap. Or they need 12 damage to kill the monster. That's not immersive. They could eventually deduce those things after repeated attempts (if they really want to) but they aren’t told those things outright.
The goal isn’t to reproduce a video game but rather replicate the tension you might experience if you were to actually encounter these things.
But to be clear, all this isn't what I'm talking about when I mean challenge. I mean in-game challenges to the characters like the monsters themselves, traps, puzzles, mysteries that require player's head to help solve. Things like hiding the system ("roll a 12 to hit," "you take 7 hit points damage") are more to do with immersion than challenge.
Look at these two scenarios, though, for how mystery and tension can be added to standard monsters:
Scenario 1:
Player: I attack the orc
DM: Ok, roll, you need a 12.
Player: I roll a 15.
DM: Ok, you hit, roll your damage. You need a 4.
Player: I roll a 6.
DM: Ok, it's dead.
Scenario 2:
Player: I attack the orc
DM: Ok, what weapon are you using? Roll to attack.
Player: I'm using my magic broadword. I roll a 15.
DM: You plunge the sword into its shoulder. Roll your damage.
Player: I roll a 6
DM: Your sword cleaves through its shoulder and down through its chest and the orc falls in a bloody heap, dead.
The first is mechanical and uninteresting. The second leaves open the mystery of how dangerous the orc was, and how difficult it would be to kill even though everyone knows
generally how difficult orcs are. If you amped or changed the stats for the particular orc, you leave open room for surprise and strangeness in the encounter -- "hey, this orc isn't acting like a typical orc!"