Android 5.0 Lollipop (API 21) is now more than a decade old. Google has stopped actively supporting it for newer Play Services updates. The error usually appears due to one of these reasons:
To understand why you need version 511743759 specifically, you must understand Google’s deprecation cycle. In August 2018, Google updated its authentication servers to require exclusively. Older Account Managers (pre-2017) used TLS 1.0 fallbacks. google account manager 511743759 android 50 best
Go to Settings > Accounts > Google and check that all sync options are enabled. Android 5