I think it’s sort of depends on the workplace culture and everybody buying in or not.
At my company, they are very strict about “just because you message somebody on slack doesn’t mean they have to respond immediately.”
The corollary is “if you don’t set yourself as away or indicate you’re on PTO, as long as it isn’t wildly outside of work hours I expect a response.”
So I have no problem sending somebody a message at 10 AM on a Saturday. Because I know that everybody at the company generally has everything flipped off. Even if they get a notification, my assumption is that they will go “oh I forgot to turn that off,” flick it off, and promptly respond to me on Monday.
Like most of these things, the devil is in the details. And if you don’t make the rules clear from the get-go, then it can be ripe for abuse and situations like you being bothered by people in the middle of the night arise.