I want to stop Apple News notifications on my Mac

This must be Unique to your computer

Start now and open an Apple Support Ticket as they are PAID  Apple Employees to deal will these types of issues .

Other location Call Centres 

 Contact Apple for support and service

There are some ( not all ) who come to these Forums seeking Technical Answers to Technical Apple Issues

Then there are some who come seeking their moment of fame 

Unlikely: are you possibly getting notification summaries from AI?

Summarize notifications and reduce interruptions with Apple Intelligence on Mac - Apple Support

Otherwise, contact Apple. With no News app installed and no notifications enabled, there’s something odd happening here.

The Apple News Application is Built into the Operating System

At least, it is installed on 4 different Apple Computers I use each will macOS 15.1 Sequoia

Check again using Finder >> Go >> Applications

You might need to erase the hard drive and reinstall the operating system. While I think the News app is installed, something must be very wrong for you to not even be able to see it.

One thing you can try is to open the Applications folder directly. No, not that one. It's fake. You need to try the Apple Applications folder. In the Finder, choose "Go to Folder" from the Go menu. Enter the following path:

/System/Applications

This will open a Finder window for the Apple applications folder. This folder shows only Apple apps. It is different from the "synthesized" version at /Applications. You should see the News app listed.

However, you also shouldn't have to do any of this. That's why I think you should re-do your installation.

Check again using Finder >> Go >> Applications

Go to System Settings > Notifications. Then find the News app in the list on the right. Select it and toggle off

"Allow Notifications".

Another way: Open the news app. Then select help in top menu and then type in notifications. A list appears. Uncheck all of the notification links for the various news medias.