It's only after everyone else went home and I felt relaxed that I finally got any of my actual work done. :(
Being in one or the other mode is normal, and not related to ADHD.
When someone relates an experience you don't understand, it's a natural reaction to assume it's actually a different experience that you do understand. I know because I catch myself doing this all the time, too. But let's understand that we have that cognitive bias and resist the temptation to "well, actually" people. (One technique that's helpful to me is to rephrase my comment as a question instead of a correction.)
As for different types of work, meetings are important and are work, but it still is frustrating when they make it difficult to get your other work done. That's not about whether certain kinds of work are legitimate. If you're late on something and you tell your manager that you had too many meetings and couldn't get into a productive flow on those tasks - that will not be seen as a legitimate reason not to have completed your assigned tasks. (Similarly, having your flow interrupted will not be seen as a legitimate reason to have fewer meetings. I've had a manager deny my request to skip a meeting - while I was fighting a production incident preventing a "must win" customer from using the product. This was something the CEO had directly told us was priority 0.) Thus, you end up working more hours, and you can't dedicate as much time to other parts of your life, like family and self care. Which can lead to burnout.
Isn't this "ADHD" everyone that has a hard time getting things done because we expect constant interruption and we got used to it?
I would have agreed a couple of years ago but since then I have become considerably enlightened about neurodiversity and how differently brains can work.
I'm not convinced that calling "ADHD" anytime we have a hard time doing something is the right way to recognize that we now live in a society that is absolutely full of small dopamine hits.
I think that's great. I'd encourage you to go looking for evidence your assumptions are wrong rather than looking for evidence that confirms it. This is a widespread misconception, so you'll find no shortage of think pieces to support your prior if you go looking for them. Evidence that this is in fact a misconception may be harder to come by, but you'll find it.
Something that helped it click for me was a friend walking me through their day step by step. In isolation, the experiences they were describing were struggles I and everyone else experiences to some degree. But seeing them arranged together made it click for me that their experience of life was just different.
I was trying to be comforting to them by telling them something like, "hey, we all feel that way sometimes, but you just pick yourself up by your bootstraps," but that wasn't the right approach because it wasn't a "motivation and discipline" issue. It was like I was giving them advice for troubleshooting Linux while they were on Windows, the machinery of their mind was simply of a different make.
Here's a metaphor that might help. It's pretty uncontroversial that cultures vary widely, and this often causes "culture shock" when visiting someplace foreign. Once I was in the Philippines, and the traffic patterns were illegible to me. It wasn't big cars in neat lanes, it was schools of motorcycles packed together and moving in all directions. I couldn't understand when it was my turn to cross the street and was almost hit several times.
If you accept that premise, is it any wonder that other people's minds would be entirely different places?
The Slack chime is a master stroke on this skit. A coworker once told me their mental health improved after they disabled the chime. (They were still responsive to messages, to be clear.)
I was a sceptic about ADHD until I read Adrian Chile's articles about his adult diagnosis [1]. I was then encouraged by those close to me to go and get checked out, and sure enough I was diagnosed (at 52). Then I learnt more about it.
The shock for me was when I filled out the screening questionnaire and mentioned to the psychologist when handing it over that "this is a waste of time, everyone would answer all these questions the same way". She gently disabused me of that notion and it turns out my answers were very different to the mean. As I became aware that most other people experienced the world very differently to me, it rocked my world.
I find the label ADHD unhelpful, personally - as you seem to. It has gone from being a pejorative label for energetic kids, to being shorthand for "I can't concentrate at the moment, give me a break", to being a middle-class lever to help your child get extra time on exams. I can't fathom this one - at school I would either finish my exam in half the time allocated, or you could give me 10 hours and it wouldn't help. What good is 30 extra minutes?
Anyway, the diagnosis has been great in helping me understand myself and others. ADHD is simply the current label for a chunk of the bell curve. There is much variation within this chunk. Neurotypicals are the big bit in the middle of the curve. I am sure that over time the definitions will become more specific and nuanced.
I don't suffer from depression anymore, seems it was simply a side effect from struggling with ADHD and "why am I incompatible with normal life".
[1] https://www.theguardian.com/society/2020/sep/30/my-treatment...
(and he has written many more since).