It seems org.gnome.Platform
changed what pixbuf loaders they ship by default.
org.gnome.Platform/x86_64/45:
$ python3 -c "import gi.repository.GdkPixbuf as pixbuf;from pprint import pprint;pprint([(f.get_name(), f.get_mime_types()) for f in pixbuf.Pixbuf.get_formats()])"
<string>:1: PyGIWarning: GdkPixbuf was imported without specifying a version first. Use gi.require_version('GdkPixbuf', '2.0') before import to ensure that the right version gets loaded.
[('png', ['image/png']),
('jpeg', ['image/jpeg']),
('ani', ['application/x-navi-animation']),
('avif', ['image/avif']),
('bmp', ['image/bmp', 'image/x-bmp', 'image/x-MS-bmp']),
('gif', ['image/gif']),
('icns', ['image/x-icns']),
('ico',
['image/x-icon',
'image/x-ico',
'image/x-win-bitmap',
'image/vnd.microsoft.icon',
'application/ico',
'image/ico',
'image/icon',
'text/ico']),
('pnm',
['image/x-portable-anymap',
'image/x-portable-bitmap',
'image/x-portable-graymap',
'image/x-portable-pixmap']),
('qtif', ['image/x-quicktime', 'image/qtif']),
('svg',
['image/svg+xml',
'image/svg',
'image/svg-xml',
'image/vnd.adobe.svg+xml',
'text/xml-svg',
'image/svg+xml-compressed']),
('tga', ['image/x-tga']),
('tiff', ['image/tiff']),
('xbm', ['image/x-xbitmap']),
('xpm', ['image/x-xpixmap'])]
org.gnome.Platform/x86_64/46 and org.gnome.Platform/x86_64/master:
$ python3 -c "import gi.repository.GdkPixbuf as pixbuf;from pprint import pprint;pprint([(f.get_name(), f.get_mime_types()) for f in pixbuf.Pixbuf.get_formats()])"
<string>:1: PyGIWarning: GdkPixbuf was imported without specifying a version first. Use gi.require_version('GdkPixbuf', '2.0') before import to ensure that the right version gets loaded.
[('png', ['image/png']),
('jpeg', ['image/jpeg']),
('avif', ['image/avif']),
('gif', ['image/gif']),
('jxl', ['image/jxl']),
('svg',
['image/svg+xml',
'image/svg',
'image/svg-xml',
'image/vnd.adobe.svg+xml',
'text/xml-svg',
'image/svg+xml-compressed']),
('tiff', ['image/tiff']),
('webp', ['image/webp', 'audio/x-riff'])]
(the python one liner is from https://gitlab.gnome.org/GNOME/gnome-build-meta/-/issues/502)