This is not accurate. First, you get one free object interaction. Second, there is no such thing as an off-hand in 5e, until you use two-weapon fighting to trigger a bonus action attack. And, then, you choose which attack is off-hand at the time of the attacks. So, in your scenario, free hand uses object interaction to unlock the door while the other makes a regular attack (or more, with extra attacks). Of course, you would need a free hand, so two-weapon fighting isn't relevant, anyway.
Free object, another rule I tend to forget about. But the idea that you can make a bonus attack with your “off-hand” but you can only swing that arm when you attack, does sometimes confuse me when their turn is spent doing something like dragging someone or grappling or something else, door was bad example.
The charmed target also can't attack the person who charmed them, which can be quite useful.
I was aware of the “gateway effect” that Banana was talking about, but completely forgot it prevents them from attacking you. Which should get added to my list I suppose.
On assassin surprise, I’m mostly with I’m a Banana.
Let’s change the language a little bit in his example.
Order of Operations:
1 - Assassin: "I’m planning on shooting my bow at the unaware guard!"
2 - DM: "Okay, the guard is surprised. Roll initiative."
3 - Init is rolled. Guard wins.
4 - DM: "Okay, the guard is not surprised anymore because of reasons. Your turn."
5 - Assassin: "Okay, I don't shoot the guard. I’ll wait til he comes back around and try and line up another shot”
6 - DM: "Uhh...okay, no combat happens, and the guard continues on its patrol, still unaware of you. "
7 - ...etc?
So here, the Assassin never declared an action, they never said they were doing something. So they are not retroactively undoing an action, just changing their mind.
Better?
Ah, but an Assassin has no way to know what the initiative result was and that they no longer have the crit… because why? Obviously they are making a different attack now than they were before, something has changed because the enemy is more alert, able to react.
And honestly, the ability to react bugs me. An assassin rolls a 37 stealth versus a noblemen in his study. Initiative is rolled. Nothing at all has happened for him to notice the enemy in the room, but suddenly he is more alert and ready to react. I can see the movie visuals you guys are talking about, but for me that creak of the bow, or glimpse in a mirror represents failing the stealth check, because now the enemy knows where you are. Not failing the initiative.