Content providers can choose what content to expose to the universal search. Most do, notably Netflix does not, so you can't find Netflix content using Siri.

That is one reason I canceled Netflix, and will not re subscribe until they opt in. Here’s the list of content providers that do integrate:

https://support.apple.com/en-us/HT208083

Android tv does. Which you can get on an Nvidia shield or a cheaper off brand device on Amazon. Just be sure to get one that is certified for Netflix. (I think it's some kind of DRM that has to be on the device for the Netflix app to work).