[cz.mafra.jizdnirady] app google login not working when using MicroG

Affected app
Name: IDOS
Package id: cz.mafra.jizdnirady

Describe the bug

The app has a google login method that shows me the microg account selector correctly populated with the one account I have logged in. But selecting it just closes the dialog and the requesting app prints an error translatable as "Connecting via external service failed."

To Reproduce
Steps to reproduce the behavior:

1. Go to the tab with burger icon (last right tab)
2. Click on user profile icon (first in the tab)
3. Click on "Google" to select a google account
4. After you select an account, the app shows an error (popup dialog)

Expected behavior
I get logged in.

Screenshots

System
Android Version: 11
Custom ROM: CorvusOS 16.8

microG
microG Core version: v0.3.6.244735
microG Self-Check results: after installing the latest the signature spoofing no longer works so that makes 3 checkboxes unticked, but they were before on 3.2.xxx and the behaviour was the same.

No source files, tests, or entry points are identified in the report. Start by reproducing the Google login flow in IDOS on Android 11 with the stated microG versions and verify the microG self-check status. Done means selecting the account completes authentication instead of showing the external-service error.