System Information
Operating system: Darwin-19.5.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 555X OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.9.15

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-08-17 19:11, hash: rBc65c66320fc8
Worked: (newest version of Blender that worked as expected)

Short description of error
In Edit Mode, selected Vertices, Edges, and Faces are not displayed as highlighted and interactive selection tools do not work.

Exact steps for others to reproduce the error

1. Open the default scene.
2. Notice that the default cube is highlighted (so overlays are visible).
   
3. Tab into edit mode and notice that it shows that 8/8 vertices are selected in Vertex Mode but no vertices are highlighted.
   
4. Deselect everything and notice that 0/8 vertices are selected and the display is the same.
   
5. Attempt to select individual vertices, edges, or faces. Notice that the selection count does not change.
6. Still in Edit Mode, select all with 'A' or via the menu and notice that everything is selected but nothing is displayed as selected.
7. Type S to scale and note that all of the vertices scale appropriately. So things are being selected via the menu but not via any interactive tools nor is the selection being displayed.