Google authenticator iOS app crash / fails to load after iOS 14.2 update

You have to reinstall the application without deleting it:

  1. Go to Settings > iPhone Storage
  2. Find Authenticator
  3. Tap "Offload App"
  4. After the process tap "Re-install App"

This provides to remove and install the application part, not your data/tokens. Your data remains.

I tried and succeeded on iPhone XS iOS 14.2.