XnView Software

you start XnView in viewer mode?

it does not matter, both modes are affected
guess issue is with reading multi-steps shortcut from .keys file

try to set 'N, N' shortcut
shortcut will be saved in default.keys
[View]
cmd_zoom100 N, N
but when app started in any mode
Settings > Interface ...

+1 I was going to make a new request for this feature but now I don't have to.

I would like to be able to change the border of the selected thumbnail to make it easier to see which image is selected in the browser.

The default border is a thin, blue line which is difficult to see, I want to make it bright pink and increase the border size to make it pop out.