OK, HEIC/HEIF images are supported in the web uploader now! HEIC photos taken with my iPhone 15 Pro work, as do HEIF photos taken with my Nikon camera. It would be great if people cant test with other photos just to make sure there aren’t any incompatibilities.
Note that these images will be converted to JPEGs, they don’t remain HEIC/HEIF files on iNat’s servers.