Incredibly well done. FWIW, the video hack is no longer needed. Originally that was required due to browsers only having hdr support with video, but recently support for PNGs were added as well. You can just use an all-white png with the rec2020 color space set.
Safari on macOS does not have HDR support in images shipping to general user channels yet.
This is probably why the emojis are working in slack, because it's just electron.