Issues, Risks and Changes have ‘Auto Notifications’ on change of 'Assigned To' which causes an issue with any workflows you wish to put on these objects. This was happening in Classic PPM, and is now seen with the Modern User Experience (MUX) where their default state sends links to Classic. Is there any solution to turn off these notifications for your users?
Release : All Supported
The only way to disable the notification is to completely turn off notifications for the particular notification type such as Change request.
Aside from the above, you could also modify the template notification for these auto-notifications. This can be changed in Administration->Data Administration->Notification. (See Configure a Notification Template for more details)