It's just a mental compartmentalization thing for me. When I want to get into slack/signal chatting mode or read messages I load such an app and look/interact. When I'm not doing that I don't want to be bothered with messages. I'm already sacrificing a portion of my life to work related tasks and being in front of a computer at many hours, when I'm not in that mode I don't want to be interrupted - people who need to reach me in an emergency have other ways to get ahold of me.

Personally, I have multiple messaging apps. I have notifications on for work slack, which is high signal, and I have notifications off for personal discord which is noisy and low priority.

I disable notifications on every app that is not on the critical path to me earning a living. Notifications are largely unnecessary. Either you are actively engaged with something, in which case you didn't need the notification, or you are doing something else and don't need the distraction, in which case you didn't need the notification. Only my employer gets a right to demand my time during work hours, which is why notifications are enabled during work hours for work apps.

We as a society have gotten way too comfortable expecting every single person to be available at all times to provide us some kind of immediate response. Let people live. If I'm hiking through the woods with my camera doing bird photography, even if you're my best friend you can wait until I get back to my car and manually check my messages, I don't need a notification. If it's an emergency, dial my number and call me, which will make my phone ring. Novel concept, I know.