How do I disable Ads on my MacOS?

There are no ads in the macOS itself. Yes, there are ads in News and the App Store. No, you cannot remove them. However, you do not have to use any applications that have ads in them if you chose not to.

I've never seen ads while using Spotlight. However, you can change what Spotlight searches in System Settings>Siri & Spotlight.

You can let Apple know your thoughts on the matter here:

Product Feedback - Apple

The ads policy and personalized ads applies to App Store and Apple services you may see in certain apps but not to macOS itself.

Spotlight can search online and as such produce ads from the online searches it makes. Those ads have nothing to do with macOS at all.

The News app may have ads for you to subscribe to the News+ service, but can be completely ignored. It has no other ads.

Adds where? If in the browser then a different story

What ads?

macOS has no ads.

Where are you seeing these ads specifically?

What are they advertising?