If you don’t want Discord to reveal your status automatically, or you would just like some more privacy when browsing your servers, you can instead set your status yourself.

There are four different statuses your Discord profile may reflect at any time: Online, Do Not Disturb, Invisible, and Idle.

If you set your account to “Do Not Disturb,” you will not receive any notifications from the server you are in, and “Invisible” will show you as offline to others even while you’re browsing a server.

Source: https://www.distractify.com/p/what-does-idle-mean-on-discord