On the Builds, GIFAnim datatypes does not exist, the problem on AmiGG happens even with earlier Builds.
On the Builds there is only GIF Datatypes, which in my opinion has a wrong Descriptor, basically the Buid's Descriptor recognizes GIF animations as images and therefore Multiview shows only the first frame.
Practically with Builds, but also with IcarOS GIF Animations are not supported, they are only recognized as simple GIF images.
On AROS One GIF Animations are well supported because I have created two Descriptors, one for just GIF images and one just for Animations (one Gif 87 and the other Gif 89), AROS descriptor includes both acronyms that's why it considers animations as images.
In my opinion AmiGG animated GIFs are not supported by the GIF datatypes, it works if you use the native AROS Descriptor which considers them Images.