By default, Gestimer displays notifications in the top right corner with the default notification sound. However Focus modes such as Do Not Disturb or Sleep may prevent notifications from being presented.
Apple Reminders Notifications
If you have the option ‘Sync with Apple Reminders‘ enabled, then you will start receiving notifications from Apple Reminders instead of Gestimer to avoid two notifications for the same reminder. Therefore please check your notification settings for System Preferences > Notifications & Focus > Apple Reminders.