Good job shopping around. Some devs don't want people looking at their files so hard they modify the file format (they swap where size and offset are stored I think but doesn't look like that's what happened here). As far as I remember webp doesn't cause problems. If the game name is known it'd be possible to take a look.
Ok, sorry for make you waiting. If you wanna check it out so here it is: https://disk.yandex.ru/d/fjAhNSOCL0LVKg