Graphics: Texture importing now strictly adheres to the supported formats in https://docs.unity3d.com/Documentation/Manual/ImportingTextures.html. Circumventing this by changing an image file's extension will no longer work. If a image file format is necessary, please file a feature request so we can look into properly supporting it.
Previously we can utilize webp files for smaller package size by changing the file extension from .webp to .png, now it is not possible to utilize webp files without having to rely on external tools.
If there is no plan to add the support I suggest revert this change as I don’t get the need to regress the workaround.
These formats were not officially supported by Unity and unfortunately this circumvention could pose a security risk. We are currently evaluating if we can add official support for more modern formats such as WebP. If you need this format, please make a feature request. These help guide us with the decision on what formats we should prioritize.
Importing these new formats at runtime would be good, but supporting them to import into a project is less important since they mainly improve compressed image size. You should not use compressed images much (ideally not at all - just PNG lossy level) in a Unity project as it will then get compressed to a GPU format.