Why do I see an update for ‘Google Play Services’ in Aurora Store & why can’t I update it?

The MicroG services app (preinstalled with iodéOS) spoofs Google Play Services & uses the same signature. Thus Aurora Store (which is a front-end to the Play Store) will show updates from MicroG services as ‘Google Play Services’, and F-Droid store as ‘MicroG Services’. As preintalled apps updates are done via F-Droid, the system will then reject the update in Aurora Store for security reasons.
If you don’t want Aurora Store to fetch updates from Google Play Services, you can blacklist the app in Aurora’s blacklist manager.