Q: Whole screen shifts sideways !!

Turn off Zoom from the Universal Access and Keyboard & Mouse panes of System Preferences.

(105103)

There is no "Keyboard & Mouse" pane, nor "Universal Access" in System Preferences.

There is "Keyboard", which has nothing about Zoom.  Nothing "zooms" when  this sideways shift happens.

There is an "Accessibility" pane with a Zoom sub-pane  but there's nothing there about shifting sideways.

Also a Keyboard sub-pane and a "Mouse & Trackpad" sub-pane, and I don't see anything there that looks

relevant

Are you using a three finger gesture on your track pad left and right to move the sceen?

No. But perhaps it happens accidentally. I guess that must be what happens. I've never tried a 3-finger swipe intentionally, but now I see what it does. Thank you!