Bottom Line Up Front - opening your message with the core request or message first - is a related practice from the military that works really well for email. https://en.wikipedia.org/wiki/BLUF_(communication)
The way I apply this to emails is to ask myself: if someone only reads the first sentence would they know what I need and if they need to act on it immediately, read it at their leisure, or file it away?
Consider all the people who are naturally inclined or conditioned to behave like the example, and then consider that many of them will miss the subtlety.
Especially those who for whom American business culture might be foreign. "Oh, they have politeness and trust-building conventions, much like we do. This is more pleasant than Hollywood led us to believe. It seems the difference is that you also verbalize what you are doing in their conventions. Maybe that's because they are a nation with a diverse immigrant mix, so they evolved that to reduce misunderstandings, and to help integrate people to common conventions. That's nice of them, and I will be sure to emulate."
I think the subtlety on that page is tuned for humor to those who already know, not to educate or persuade those who don't.
People, particularly family, calling me on the phone and then asking me what I'm doing as if it's any of their business and it's their decision whether what they need is more important than what I'm doing is such a pet peeve of mine.
I admit to being guilty of the "YT?" or "Hi" type messages, but it's for a reason: the person may be presenting to a client and shared their screen instead of their window.
I've been on too many Zooms where the presenter's Slack pops up saying, "John, we have a call with <company name> about <topic> at 3:00. Can you join?"
Multiple times, this information was probably sensitive. I'd rather avoid that by waiting until I get a response.
But you can expect people to do their jobs. If a notification embarrassed the company in front of a customer then talk to that person's manager about training them to not be a numpty.
Stop having such low expectations of grown ass adults.
You clearly haven't worked at a job with incompetent adults before. I mostly haven't either thankfully, but my wife just put in her two weeks resignation after two months at her new job because she works proposal management and she couldn't get anyone to do anything properly (proposal management requires getting information from other people in order to put together a proposal with all the information requested), while they just kept piling enough work to keep at least 3 employees busy on her.
Forms filled out wrong after explicit instructions, vital information needed for a proposal due at 10 in the morning not received until 5pm the day before (and even then it's missing half of what they were told was needed), and then after asking for it again, finding out half an hour before it's due "oh I'm out running an errand, I'm not in the office, I can't get that to you", people taking pictures of handwritten notes in sloppy handwriting and sending them to other coworkers instead of typing them up themselves, people refusing to click a link on their iPads to access a document and demanding email attachments instead, people refusing to store important documents in CRM tools and instead saying "well it's in someone's email somewhere".
She's worked with several of these types before, but not this many people at one company, and not with such an intense workload (I think she was expected to submit a proposal every other day this month while wrangling these people, which is very short. At past jobs she usually only had to juggle 1 or 2 proposals in any given week).
She had no choice but to work holidays and nights and weekends and it still looked like she wasn't doing a good job because they weren't doing their jobs (her boss knew she was though, since she had to do the job before she was hired and knew what it was like, and begged her to stay).
I guarantee none of these people would have bothered turning off a notification, and then something confidential (legally not supposed to be seen by certain employees) could have been revealed.
Not that I ever usually bother to think about that myself, personally. It's rare that I start a conversation with someone with 'Hey blah! Here's some information that I can get in trouble if other people besides you see!'
There may be a middle ground. In this example, you could say, "Are you available to join a call at 3:30?"; that gives a little information about the topic and the time sensitivity, but it may still require a follow-up.
At one point I installed a filter on my IM client to silently discard trivial messages like "thanks" and "OK". There were already delivery indicators so nothing was lost.
Perhaps a hello filter and "yes?" auto responder could help, at least during business hours. Then send an OOO message if after hours.
The way I apply this to emails is to ask myself: if someone only reads the first sentence would they know what I need and if they need to act on it immediately, read it at their leisure, or file it away?