Hotkey >> Z (during draw)
Purple cut is inset. This will slice the mesh, add a solidify and push the mesh inwards.
Since this uses the solidify large values will get problematic.
Pressing T during operation will adjust the thickness but also pressing D or Ctrl + D brings up the mini helper for fine adjustment.
Inset has inset slice and recut as alternative behaviors modifying inset.
Things to be aware of with inset.
Inset has it's own playlist which can be explored below. There are multiple aspects to be aware of with inset to get the most out of it.