>Limits inherited from the fact it's basically a video codec

It's also disappointing for a video codec released in 2018. For context, in 2019 Sony released an 16k screen. Granted, that was a home cinema screen, and 16k displays will be a niche product for the forseeable future, but it's also not something unimaginably large.

It's still a perfectly valid bitstream and file if you don't conform to the defined profiles and encode resolutions up AV1's maximum 65536x65536 (or even larger with HEIF grids), as long as you don't falsely claim you're conforming to the defined profiles/levels. Then there's simply no guarantee that any specific decoder can decode it. (but technically that's the same with merely conforming to the advanced profile, or else there wouldn't be two profiles...)

I don't know about the libavif API, but certainly libavif's avifenc will happily create large files that don't conform to the AVIF advanced profile.

Is that a limitation of the format itself, or just a limitation of libavif?

Is the 8k limit both horizontal and vertical?

Most of my panoramas are horizontal (15k x 4k), but a few are vertical.

How is 32 bits not enough ?