Android Auto has had a long history of breaking on Samsung smartphones. Although Google is quick to issue a fix, it only acts as a bandage over a festering wound that clearly requires more care.
This time around, several Galaxy S21 users reported that their devices weren't working properly with Android Auto. Google promised a fix with the July security update, but that never happened, by the looks of it.
The issue won't be fixed before September
Instead, Samsung has pushed back the update to September, as seen on the official Google support forums. It also states that the fix will arrive as a standalone update, and not bundled with the September security patch. It effectively means that Galaxy S21 users are stuck with a buggy version of Android Auto for nearly a month more.
Currently, there is no workaround that appears to fix the problem. Regular troubleshooting steps such as uninstalling and reinstalling the Android Auto app and even factory resetting the phone seem to do little to alleviate it.
However, there could be more to it than just buggy Android Auto interaction. Several users on Reddit said that they have had no trouble running the software on their Galaxy S21 units.
In all likelihood, only specific car models may have been affected. Nonetheless, it is a bug that needs fixing, and we can only hope that Samsung gets around to it sooner, rather than later.