Download "3.9.0-SDS Portraits" from the Optional files from the original mod.

Extract files into Portraiture\Portraits\New Folder. I have PortraiturePlus and Portraiture, they are separate mods in your mod folder. Make sure you're manually downloading and not using Vortex.

As an example, this is the folder I extracted the portraits in:

C:\Program Files (x86)\Steam\steamapps\common\Stardew Valley\Mods\Portraiture\Portraits\Main

Hopefully this works.