Is there a way to remove the Disa's icon on the status bar? It stays and when I scroll down to see, it says "Everything is running smoothly".
Can we remove this and have this icon only when I receive message?
According to Disa FAQ that's foreground feature.
The persistent notification is created by the Foreground setting, found in the General tab of Disa's settings. If your device is fairly new and has plenty of free memory then this setting does not need to be enabled. If you choose to disable it remember to restart Disa for the change to take effect.
The persistent notification was enabled by default for older devices which cannot run Disa in the background without it. However, if you feel that everything is working fine, i.e. you are not seeing the splash screen every time you start up Disa and/or you have no delayed notifications or missed messages, then you can turn this off in Settings.
Go to the General tab and then untick Foreground. You may need to restart Disa before the notification goes away;
Note: Some devices (EMUI, OxygenOS and devices without Google Play Services) get delayed messages without this feature enabled.