The Quick Access Bar is just below the Viewport. As mentioned above, it has two states, standard and simple UI. A different set of icons is displayed, depending on the which state you are in.
These are the icons you will see when in Standard UI mode.
Graph - Opens the Scene Graph.
Transform - Opens the Transform module.
Materials - Opens the Material Editor.
Curves - Opens the Curve Editor.
Render - Opens the Render Settings.
Cameras - Opens the Camera Editor.
Clips - Opens the Clip Maker.
VSets - Opens the Variant Sets module.
Sceneplate - Opens the Sceneplate Editor.
UVs - Opens the UV Editor.
These are the icons you will see when in Simple UI mode.
Assets - Opens the Asset Manager, which contains tabs for loading geometry, materials, and environments.
Scene - Opens the Scene module, which contains tabs for the Scene Graph, Materials, Environments, Camera, Lights, and Settings. Some of these tabs will also have their own Properties section.
Animation - Opens the Clip Maker.
Variants - Opens the Variant Sets module.
Render - Opens the Render Image module.