No push notifications from authenticator app when switching to Azure AD B2C direcories

You may take a look at the following area:

1. Check MFA settings in Azure AD B2C:
- Go to your B2C tenant in the Azure portal.
- Navigate to Authentication Methods.
- Ensure Microsoft Authenticator push notifications are enabled for your user flow.

2. Re-register MFA for the B2C account:
- Remove the B2C account from the Authenticator app.
- Re-add it by signing in through a protected app or portal that triggers MFA setup.

3. Use Conditional Access Policies:
- If you're using custom policies, verify that push MFA is allowed and prioritized.

4. Fallback Options:
- Unfortunately, B2C login flows may not always offer alternate MFA methods (SMS, call, email) unless explicitly configured. You may need to adjust the user flow or use a custom policy to expose those options.