How to integrate firebase/angularfire with Nx

I am try to use firebase (angularfire) with Angular/Nx. I found the plugin @nxtend/firebase.

https://nxtend.dev/docs/firebase/getting-started/

When trying to add it via ng add @nxtend/firebase I get the following error: An unhandled exception occurred: Schematic "ng-add" not found in collection "@nxtend/firebase".

The next command gives another error: nx generate @nxtend/firebase:init Error: Unable to resolve @nxtend/firebase:init. Cannot find generator 'init' in ....\node_modules@nxtend\firebase\collection.json.

I am using @nrwl/workspace": "12.9.0" - and Angular 12.x

Now my Questions:

1. How to fix that?
2. Can it be that @nxtend/firebase": "^11.1.2" ist not compatible with Angular 12.x?

And most important: 3. Ay suggestions how to integrate firebase/angularfire with Nx? Because unfortunatelly this seems to be a complicated task...