Image styles - thumbnails are broken in config page when private file system is used and if effect "Convert" in use

I think I have to modify this.

It is when i have Convert: webp or anything else in my image style that the sample is not there.

In case it can help, I had a similar problem because the private image access system denied access to the thumbnail (403) because the image was not used in any viewable entity for my user (until I gave the "view config page entity" permission).

I also had another problem because I used the Webp contrib module before, which had created .jpg.webp files in the uploaded images private directory. Then I uninstalled Webp to use the core convert system. With this new system, it's not expected to have converted .jpg.webp files in the uploaded images private directory. These files should only exist in the styled (derivative auto-generated) images private directory.