I am trying to test android deep link urls through adb to launch my app

You don't need to specify full path to your activity, but if you want to test whether you react properly to URI in your app just specify app package:

adb shell am start -a android.intent.action.VIEW -d "example://gizmos" com.myapp

Also there is bug in command you provided - there should be example://gizmos not example:gizmos

Here is the command

adb shell am start -d your-deep-link

Example

adb shell am start -d rm://yoursettingpage/v1

The best solution for android studio is explained here: https://code.tutsplus.com/tutorials/how-to-enable-deep-links-on-android--cms-26317

TLDR : Android Studio --> Run --> Edit Configurations

Change Launch in Launch Options to "URL" and enter in the text field URL the correct url: "something://"

As the other answer mentioned, it should be "example://gizmos" and not "example:gizmos"

Alternatively, instead of using adb, you can test deep links directly on android using deep link tester app:

https://play.google.com/store/apps/details?id=com.manoj.dlt

No need to mention any package name or component name. Just type the deep link and fire.

I've found testing deep links through adb to be cubersome and difficult at times. Hence, I've built this small app to do it.