No one has any plans to decode AVIF still images in hardware. There are two problems. The subset of AV1 supported by hardware is much narrower than what is in practice used in AVIF images. Such images cannot be decoded by hardware. Second is that it actually doesn't get you any speed. Each image would need to be shuffled to the GPU, decoded, then sent back because browsers aren't really set up right for doing everything on the GPU. And any non-stateless HW decoder would be problematic, since every single image would need to reconfigure the decoder state, which is slow.
This isn’t a problem on any mobile SoC because “sent to the GPU” doesn’t mean anything on a unified memory system. (And Safari does use hardware image decoding.)
The majority of AVIF images are hardware decodeable, even if most viewers don't bother with it. The biggest limitation is that profile 0 decoders are 4:2:0 only, but that describes the majority of Web images.
Krita, GIMP, DarkTable, Affinity, and freaking Adobe are just "some" image viewing programs to you?
Adobe supports it... for importing, but you can't export to JXL. You can count plenty of obscure photo formats like JPEG 2000, IFF, PCX, OpenEXR, etc. in that category.