update to androidx Unfortunately you can't have non-Gradle Java modules and Android-Gradle modules in one project. code example

Example: capacitor-android. Unfortunately you can't have non-Gradle Java modules and Android-Gradle modules in one project

1- close the project

2- close Android Studio IDE

3- delete the .idea directory

4- delete all .iml files

5- open Android Studio IDE and import the project

Answer from here