[zinekeller]

> and the maximum dimensions of a coded image is 65536x65536

As pointed out in another comment, this is less of 65536 by 65536 and more of 65536* by 65536* if you followed some more complicated steps. Considering that the original JPEG supports that without relying internally on multiple images (the trick AVIF used to "support" the full 65536 by 65536), it seems not suitable for software which writes images in one pass.

[brigade]

No, it's AV1 that uses (up to) 16-bit fields for image dimensions. HEIF grids, which is the AVIF feature that combines multiple AV1 images into one, have 32-bit fields for dimensions so are limited only by what the decoder is willing to allocate.