I just try this type of image. I created simple blog post and add avif image inside and get error.
Given type (avif) is not valid
Type error cannot convert undefined or null to object
at function keys
at https:// .com/user.plugins/admin/theme/grav/js/admin.min.js
@alfabuster, Have you already consulted the docs? Especially the section about Supported Media Files?
Yes. I read this. According this article in the file system/config/media.yaml full list of supported mimetypes. In the file I found
png:
type: image
thumb: media/thumb-png.png
mime: image/png
webp:
type: image
thumb: media/thumb-webp.png
mime: image/webp
avif:
type: image
thumb: media/thumb.png
mime: image/avif
PNG, Webp works fine. But avif got error.