XnView Software

All image are opened properly when I open them with XNview, except for WEBP: when I double click on a WEBP, it opens XNView with an empty tab.

I've tried the "set file associations" button in the setting with xnview as admin, doesn't work: it brings the "to change your default app" message, I attached a screenshot.
I've tried resetting "default app" the windows settings and setting xnview again, doesn't work.

I've had this problem for a long time now.

do you have installed the setup?

Yes, I just upgraded to 1.4, still the same problem.

I tried to do it with "Associate files with XnViewMP.exe" as admin, same result (screenshot).

You need to use Windows and not "Associate files with XnViewMP.exe"

I already tried

HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Explorer\FileExts\.webp\UserChoice seem a bit messed up

I gave up and installed irfanview, sorry

Ok so I selected the "Associate files with XnViewMP.exe" in the "default app" section, for pictures, since xnview was not appearing as a choice.

Previously I was setting individual file extension in the "choose default apps by file type".