Hi cositsking, the ‘repeat last operation’ is not available in Sculpt Mode. (Making a stroke with a brush is not an operation…)
When in Sculpt Mode (and sculpt changes (meaning mostly: getting new features) very fast per Blender Version) CTRL+R activates the Remesher and SHIFT+R shows that grid with the resolution of the Remesher and you can move the mouse to interactively change that resolution: left-right changes it ‘normally’ and up-down changes the resolution in smaller increments.
