The ability to reach you instantly does not create an obligation to answer instantly.

Reachability has been mistaken for availability. Because a message can arrive at any moment, people feel bound to respond at any moment, and the expectation has never actually been agreed to by anyone. The technology creates the possibility, not the duty. Confusing the two is how a great many people lose control of their attention.

Decide your own response times and keep them roughly consistent so people learn what to expect. Turn off the notifications for whatever does not need immediate attention. Almost nothing gets worse for a few hours of delay.