I used to use category icons with a transparent background (especially useful when having both light and dark mode versions). Now I always get a white background. I realized that when I download an old icon (that still works) it is PNG. But when I download the newly uploaded (PNG) icon, it downloads as JPEG.
I would consider this a bug as I think it makes no sense to convert those icons to JPEG. I have full control over what I am uploading, unlike in forum posts where I can imagine it can be useful.
EDIT: This worked Problem with category image transparency. I did not find it at first. But what has changed recently? My png_to_jpg setting was on 95, so changed to 100 and it started working. But why now?