First, delete current ARCoreExtensions from the project using the package manager.
Install the new version by following this tutorial.
Choose ARFoundation 5.x even if Google’s docs suggest matching ARFoundation versions
if you already have External Dependency Manager installed in your project for example as a dependency of some Firebase package, you want to download a version without EDM4U, otherwise you will have a conflict
If their provided link doesn’t work, search for “ARCore Extensions without EDM4U release” on Google. The first GitHub link typically has the correct package.
In some cases, the “com.google.external-dependency-manager” file will download as a .tar instead of .tgz. If that happens, Manually rename it to .tgz before adding via Unity’s Package Manager or you will not see the option.
Delete the Assets/ExtensionsAssets folder. This is an important step.
Make sure that the ARCoreExtension object in your scene still has the XROrigin set.
Go to Project Settings - XR Plug-in Management and make sure Google ARCore is set to true under the Android tab. Make sure that ARKit is set true under the Apple tab.