SCCM Always On Groups on SQL 2016 Standard or SQL 2017 Standard

When you are planning to configure SQL Always on for SCCM, make sure you will use SQL enterprise edition instead of STD.
SQL 2016 and SQL 2017 standard editions offer's only basic Always On Availability Groups, unlike Always On Availability Groups.

Basic Availability Groups has various limitations and one of them is no read access on secondary replica. For ConfigMgr it is required to have read access on all the replicas. Because of this limitation SQL 2016 standard or SQL 2017 Standard editions wont support ConfigMgr always on availability groups.

For further details refer to Microsoft Basic Availability Groups