Out of all of these things, open offices have been the worst in my opinion. At least with slack (or whatever other messenger you use) you can ignore that until your thought is complete or you want to make a quick note of your thoughts before allowing the distraction. When someone taps your shoulder it's much harder to ask them to wait, so it happens much less than it should... not to mention the constant passive distraction of people moving around and having other conversations.
We used to be in small offices of 2-4 people. That was perfect and I miss those days. The office looks a lot nicer now that it's open, but it's a disaster from a concentration standpoint. But, I think a lot of managers like the open concept because it's easier to see people and because it does often look nicer and often has more natural light.
I have never worked in a 2-4 office and certainly not a 1-office, but I find about 10 in an office is manageable if they are all quiet non-phone-calling people.
I worked a place with 400 people in open plan close proximity, where your workspace doubles up as a corridor, and no meeting spaces, so it also doubles up as a meeting room for any teams meetings. It was impossible to concentrate. That drove me to some Howard Leight earplugs, beefy headphones with "the ocean machine set to 9". The impomptu meetings now sounded like a squeek, but it was still distracting.
I had to leave that job because of this and other negative effects of a cattle-like approach to handling software talent.
We used to be in small offices of 2-4 people. That was perfect and I miss those days. The office looks a lot nicer now that it's open, but it's a disaster from a concentration standpoint. But, I think a lot of managers like the open concept because it's easier to see people and because it does often look nicer and often has more natural light.