react-native link only for one project (Android or iOS)

if react-native < 60

1. rename platforms ( iOS or Android) that you don't want to link.
2. run react-native link your-library-js-package-name.
3. rename platforms to the original name.

.

react-native >= 60

because the new react-native versions have some auto-linking feature you should tell the react-native CLI to do not link your library:

1. create a react-native.config.js file in the root of your project.

2. add some config like this

   module.exports = {
     dependencies: {
       'your-library-js-package-name': {
            platforms: {
              android: null, // assign null to disable autolinking
              ios: // assign null to disable autolinking or remove the 
                   ios key to let do the default linking
           },
       },
   
     },
   };
   

check this for more info docs

You can choose to link libraries for only a certain platform by doing:

For Android: react-native link (your_library_name_here) --platforms android

For iOS: react-native link (your_library_name_here) --platforms ios