You can disable notifications for the Insight Timer app directly from your device settings.
For iPhone (iOS)
Open your device’s Settings.
Tap Notifications.
Scroll down and select Insight Timer.
Toggle off Allow Notifications.
You can also customize notification types (Lock Screen, Banners, Sounds) instead of turning them off completely.
For Android
Open your device’s Settings.
Tap Notifications (or Apps, depending on your device).
Select App Notifications.
Find and tap Insight Timer.
Toggle off Allow Notifications.
Notification labels may vary slightly depending on your Android version or device manufacturer.