[com.nianticlabs.pokemongo] Google sign-in immediately fails and "Unable to authenticate"

Affected app

• Name: Pokémon GO
• Package id: com.nianticlabs.pokemongo

Describe the bug

• When trying to log-in with Google, Pokemon GO fails and says "Unable to authenticate. Please try again."

To Reproduce

1. Start Pokemon GO
2. Fling the date of birth year randomly to 1980 or something 18+
3. Tap either Returning or New Player
4. Tap Sign in with Google
5. "Unable to authenticate. Please try again."

Expected behavior

• Pokemon GO to report the Google account email briefly confirming the sign-in, and to continue loading the game

Screenshots

• https://i.imgur.com/G9jGG8V.mp4 (50 second on-device video showing microG status, account, and PoGO error)

System

• Android Version: 20
• Custom ROM: LineageOS for microG (lineage-20.0-20230704-microG-enchilada)

microG

• microG Core version: 0.2.28.231657
• microG Self-Check results: All ticked

Additional context

• Happens with Ingress too (another Niantic game)
• I don't believe this interacts directly with Play Store Games for achievements or anything; it just uses Google for the log-in authentication
• My PoGO account with Google sign-in is active, not banned, isn't restricted in any way afaik, and worked fine with Gapps a few hours ago today
• Pokemon Trainer Club sign-in and seemingly PoGO itself work fine with microG. I would like the Google sign-in to access my main PoGO account and I don't believe I can convert it to another sign-in
• https://github.com/microg/GmsCore/issues/1774 indicates Google sign-in worked for them

Start by reproducing the Google sign-in flow in Pokémon GO on LineageOS for microG with microG Core 0.2.28.231657, following the listed steps and checking the comparison with issue 1774. Done means Google authentication succeeds and the game continues loading instead of showing “Unable to authenticate.”