>Is it DnD for players to be able to jump clear over the head of the enemy he has engaged to land behind him, and as the enemy watches you helplessly (due to it being turn based and it's not his turn to move) as you stab him in the back?

Yes, DnD is also turn based. you can do both of these things in DnD. Tho the first one is probably a difficult acrobatics check that either lets you land on your face or get an opportunity attack, but its still something you absoluteley can do with the apropriate skillset.

>Is it DnD to be able to go invisible and then push an enemy that is twice your height and weight to his death with 100% chance of success?

i dont know where you get the 100% chance of success but tripping a troll of a bridge probably happens in every second campaign.

>Is it DnD for a character with 17 STR to be able to pick up an enemy, with perfect acquiescence from the latter, and then hurl him clear across the room? Mind you, the enemy cannot even do anything to stop you from lifting him up. Is this how DnD is played?

a character with 17 STR is jacked as shit, have you never watched wrestling as a kid? or done Judo?

>Is it DnD for low level goblins to shoot fire arrows that, even when they miss you, light the ground beneath you on fire and do guaranteed unavoidable 2D4 damage?

onward to my goblin Slayer example.
Dont roll the dice, play smart. sounds pretty much in line with that.

I dont have much time right now to dedicate to play Baldurs Gate 3 or any video games for that matter. So id like some concrete examples how to get to those outlandish situations.