What is meant by "no need to move sd card share the same disk with os"?

I am using Redmi 9, 4/64, Android 11, MIUI Global 12.5.3. I was trying to move apps from internal to sd. But there was no option, though i enabled it in developer settings. I tried some app and they either showed **move to sd not supported in this device** or **no need to move sd card share the same disk with os**. So, how this works? If i run out of internal storage eventually, next will my sd card be used to store apps? Is there any way to move to sd?