This object indicates the IPv6 access list is extended ('true') or standard ('false'). A standard ip access list means only IPv6 address related i.e. source or destination IPv6 address is specified for the filter. For an extended IPv6 access list, more fields can be chosen for the filter.
Sources for this description
D-Link official switch MIBsD-Link MIB copies (LibreNMS/Observium Community)