Can I use library that used android support with Androidx projects.

You can enable Jetifier on your project, which will basically exchange the Android Support Library dependencies in your project dependencies with AndroidX-ones. (e.g. Your Lottie dependencies will be changed from Support to AnroidX)

From the Android Studio Documentation (https://developer.android.com/studio/preview/features/):

The Android Gradle plugin provides the following global flags that you can set in your gradle.properties file:

• android.useAndroidX: When set to true, this flag indicates that you want to start using AndroidX from now on. If the flag is absent, Android Studio behaves as if the flag were set to false.
• android.enableJetifier: When set to true, this flag indicates that you want to have tool support (from the Android Gradle plugin) to automatically convert existing third-party libraries as if they were written for AndroidX. If the flag is absent, Android Studio behaves as if the flag were set to false.

Precondition for Jetifier:

• you have to use at least Android Studio 3.2

To enable jetifier, add those two lines to your gradle.properties file:

android.useAndroidX=true
android.enableJetifier=true

Finally, please check the release notes of AndroidX, because jetifier has still some problems with some libraries (e.g. Dagger Android): https://developer.android.com/topic/libraries/support-library/androidx-rn