In the upper left corner of the screen, look for the menu item that says "Safari" and select it.
One of the first options in the drop-down menu should be Preferences. Choose that option to get started
Choosing Preferences will open a new window with all important Safari settings.
Go to the upper part of the window and choose the option that says Websites.
Now, look at the sidebar menu on the left, where you'll see many different options for controlling how websites deal with various macOS features
Scroll down until you find an option for Notifications and select it.
This will open a section in the middle of the window that will show you all the websites that have requested permission to send notifications to your operating system.
Here you can select each website and change its settings to Allow to activate all notifications.