I'd rather we taught people not to start a messaging/slack/teams/whatsapp/etc session with "hello". Don't say "hello" and then make people wait for however long it takes for you to type whatever it was you really wanted to say. This isn't a telephone. Stop trying to use async comms as if they were synchronous. It's rude and annoying.
I find this trends pretty well across generations - young people are rarely starting with "hello". I suspect people above a certain age just find doing it that way more polite
https://www.nohello.com/