What I miss most is being able to go to the bathroom alone
Seriously. Used to just close a door for 5 minutes and have peace. Now there's always someone asking where I am or knocking asking if I'm coming out soon. Or just standing there waiting. I don't know when I became the guy who gets excited about taking a long shower but here we are.
Bathroom privacy. That's the real thing nobody warns you about before you have kids. I just accept now that the door is staying open and someone's asking me stuff through it.