I set expectations with my team that it's only an emergency if I call or page them. I don't have Slack notifications on in my personal time, I don't expect my team to either.
I miss async communication. People apparently think it’s rude if I slack them at 4 AM but it’s on them to turn off notifications. I don’t even have slack on my phone. Nevermind people complaining about out of hours emails.. just don’t read them!
The few times I had to Slack someone way out of office hours I simply set a delayed message to be sent in the beginning of the workday.
People have different notification management than we do, I disable any work-related app notification outside of 9-5, others don't so maybe it's better to cater to them and send delayed messages if you aren't expecting them to read right away.