Collections replaced Layers. Yet, Layers are still there (presumably for backwards compatibility). It seems Layers and Collections are related, e.g. Collection 1 = Layer 1, etc.
Problem 1: Whenever one press a number key by accident, all objects in Collections are unchecked (hidden). Only objects in Layer is displayed.
Problem 2: Blender does not remember what items in Collections were checked before. To display required items again, one must manually open each Collection and recheck items as needed. A tedious task, especially if Collections are nested.
Problem 3: Collections are far superior to Layers. But there seems to be no way to disable the Layers system to prevent the issues above.
Problem 4: Layer buttons does not seem to be defined in the Keymap, as if they are hard coded. If they can be shown in the Keymap, one should at least be able to prevent accidental number key presses by disabling the Layer shortcut keys.
If anyone knows of a way to disable the old Layers system, or how to disable the keyboard shortcut keys for Layers, I would love to hear about it!
Update: I installed Blender 2.83.3 when it was released. Sadly, the Layers panel was still there.
I had a number of add-ons installed which i did not need anymore, and disabled them all. To my surprise, the Layers panel disappeared in the process.
Trying to determine which one was causing the Layers panel to appear, I re-enabled all the add-ons. It did not re-appear. I'm stumped.
Anyway, I think all the major issues I raised in this thread has been resolved.