The Milio build for Support is Shurelya's Battlesong, Ardent Censer, and Moonstone Renewer. This LoL Milio guide for Support at Platinum+ on 14.3 includes runes, items, skill order, and counters.
Milio Counters
51.5%
(-0.2%)
42.0%
(-1.1%)
4.9%
(+0.1%)
2.0%
(+0.3%)
188
(+5)