A comprehensive guide to fixing the "Hidden 5GHz SSID" problem on Samsung Galaxy devices (S25 Ultra, S24, etc.), specifically for users in South Asia (Bangladesh, India) using Xiaomi/Mi Routers.
Samsung devices apply regional software locks based on the inserted SIM card. In many regions, the phone's modem is restricted from "seeing" lower 5GHz channels (36–48). If your router is set to these channels, the 5G network simply will not appear in your Wi-Fi list.