Thank's to all participants
a way to solve is chrome extension Save as, which allows to select the type image while saving.

@leocg ok, got it, thank you
How can i disable webp support in opera with some settings or tweaks?

even when trying to save as

vpn and all plugins are disabled

@yanta said in Downloaded Image Auto Become .webp:

Perhaps the reason for this behavior is the way the website operator provides images on the respective website.

@sgunhouse No. Opera saves images as webp even any saving modes are disabled, even in win10