Hi,
I’m using the iCloud integration for some time now and I have this ‘issue’ for some time too.
I get the following error a few times per day.
2021-03-21 06:07:25 ERROR (SyncWorker_12) [pyicloud.base] Authentication required for Account. (421)
Around the same time (give or take a minute), I also get an e-mail from Apple that there was a login via a webbrowser.
Is this normal behaviour for this integration?
I’m running the current versions of everything: (HA 2021.3.4 at moment of writing)
I tried removing the integration and deleting the icloud directory in .storage before reinstalling as per the documentation, but that didn’t resolve it for me.
Background info. I’m not sure if this is at all relevant, but maybe it is 
I had some issues during the initial installation with a prior version, which, from top of my head, had to do with the 2FA part. I also tried installing a HACS module (called icloud3) at one point, which supposed has more functionality than the official integration, but the installation/configuration was way too complex/cumbersome to go on with it for me (the quick start guide is the longest I have ever seen)