XnView Software

XnViewMP 1.6.5 64bit
Windows11 (23H2), display resolution 3840x2160, win scaling 150%

Shortcuts - zoom
Once you start zooming, default shortcuts do not allow you to return to the default state - 'Fit image to window, large only' (aka 'Best fit').
Some other apps have such shortcut:

Suggestion

• reassign / key
  from 'Fit image to window'
  to 'Fit image to window, large only' (aka 'Best fit')
  
  so user can always return to the default state

Related

• suggestions
  Shortcuts - general - assign F1 to About
  Shortcuts - zoom - reassign / key to 'Best fit' (current post)

See issue for current status and some details.

This problem is supposed to be fixed in XnView MP 1.7.0. Please check and confirm the bug fix here.

fixed in 170