adb shell am start -W \
  -n <package_name>/<fully_qualified_activity_name> \
  -a android.intent.action.VIEW \
  -c android.intent.category.BROWSABLE \
  -d "<deep_link>"

-W – Blocks activity manager (am) until the launch is finished (or times out) and then prints timing/status info.
-n – Sets the explicit component to launch. Ex: com.mypackage/com.mypackage.MainActivity.
-a – Sets the intent action.
-c – Sets the intent category.
-d – Sets the intent data. Can be anything that the app is configured to handle. Ex: https://mysite.com?action=1