1) Open the Settings dialog from the right-top gear button.
2) Uncheck the "Notify me when a new product patch is available." It will disable the notification when a new product patch is released. You can still use the "Check for Update" from your product Menu > Help and get the latest version.
3) Uncheck the second "Show important product notifications." It will disable all the product release notifications and some discount messages.
4) If you don't always want the Reallusion Hub in the background, then you can uncheck the third checkbox "Run Reallusion Hub when my computer starts". This will not affect your program usage.