Reply To: Why does my cube with Subd modifier wont distort when I try to sculpt it with the brush?

If you see the original 8 verts in sculpt modes it means that you haven’t applied the modifier before entering sculpt mode. This can also be confirmed by looking at your modifier properties. If you still see a subsurf modifier present, it means that it hasn’t been applied. 

“Applied” could be the confusing word here. Adding a modifer to an objects isn’t technically “applying” it in the Blender sense. In the video I clicked the Apply button on the subsurf modifier before jumping into sculpt mode. In 2.9 it’s a little different: There’s a dropdown arrow with the apply option:

Once you apply the modifier, you’ll see it disappear from the stack and your hi-resolution mesh will be sculptable in sculpt mode.