told? by who?
are you referring to the mainboard specs or to someone who told you something?
visite the manufacturer website and check the mainboard specifications in terms of ram
http://www.asrock.com/mb/AMD/AB350%20Pro4/
there it says this
AB350 Pro4
ASRock Super Alloy
Supports AMD Socket AM4 A-Series APUs (Bristol Ridge) and Ryzen Series CPUs (Summit Ridge)
Supports DDR4 3200+ (OC) (Ryzen CPU) / 2400 (A-series APU)
2 PCIe 3.0 x16, 4 PCIe 2.0 x1
AMD Quad CrossFireX™
Graphics Output:HDMI, DVI-D, D-Sub
7.1 CH HD Audio (Realtek ALC892 Audio Codec), ELNA Audio Caps
6 SATA3, 1 Ultra M.2 (PCIe Gen3 x4), 1 M.2 (SATA3)
8 USB 3.0 (1 Type-C, 2 Front, 5 Rear)
Realtek Gigabit LAN
or they are lying you or there is a error in names
i personally don't like much asrock, i do prefer msi, but it also depends on your budget and if you are doing a themed white pc as seems to be the case here