XnView Software

When navigating among the images in browser with arrow keys tooltip randomly popups after a short delay.
Sometimes for the previously selected file.

I think you need to check "View->Only one window view opened".
By default XnView will create a new view window (which is shown on the tab bar if tab bar is visible) for each viewed image.

Main menu seems to be somewhat empty while there are many of long nested submenus.
I would make sense to move submenues such as "View->Sort by" "View->Filter By" "View->Columns" "View->Layout" to the main menu.

I consider 1-pixel contrast border to be enough to separate UI elements.
But XnView is cluttered with borders and padding of all kinds.
The padding on the right side is especially annoying as it forces user to carefully position cursor to use scrollbar.
On this image i've highlighted problem areas ...

I was going to post about the lack of WebP support as well, but it turned out that all I had to do was to download Extended installer and mark WebP plugin for installation.