Use native Google Account Picker with B2C
You can create a resource owner password credential (ROPC) flow that enables a native app to collect a user credential and exchange it for an ID token, an access token, and a refresh token with the Azure AD B2C tenant.
These Android and iOS samples demonstrate how you can integrate an Android or iOS app and the ROPC flow using the AppAuth SDKs.
It seems the scenario you are trying might not work with B2C or any other Identity products, You can try the below link to integrate B2C in android with opensource package.
https://azure.microsoft.com/en-in/resources/samples/active-directory-b2c-android-native-appauth/