Flip canvas> To Reverse Horizontally and clear layer function

Hello,

1. How do I flip the canvas without ruining everything? (it should not be recorded in the hisotry), the feature should be called REVERSE VIEW HORIONTALLY

Right now there are no image flipping implemended for artists, as I understand.
I'm working on 20 000 x 20 000 px. canvas and I zooming in for 1000 x 1000, if I flip canvas horizontally I will just send my image to the other side of the canvas and will see a totally diferent piece of art, when I need to reverse the view horizontally, where the anchor point is in the middle of CURRENT area you see on the screen.

This is a very simple feature, which is implemented in all drawing apps, but not in PS? Why? Why? Why?

2. How do I clear the layer?

And yet again, there are no such function in PS for some reasons you don't want to add it.

The key for clearing the layer should clear the layer of all pixels, without deleting it.

NO actions are not a solution and NO pressing ctrl + A and hitting delete is not an option.

I need a working key, which will CLEAR the layer with one motion.

Why this is so hard to add, why need to update softwere adding features nobody needs, but skipping the basics? Why? Why? Why?