Does the custom emoji in this font basically look the same as the same character in other fonts, e.g. a thumbs up emoji (👍) but the custom one has an extra large thumb? If so, then something like <span aria-hidden=true>👍</span> is the way to make it decorative.
If the custom emoji is not equivalent to an existing emoji in the Unicode catalog, then the font should have it assigned in the Unicode Private Use Area (PUA) Peter Krautzberger (npub1t46…wpm3) referred to. Screen readers shouldn't say anything when they encounter PUA characters, they don't have a name stored for them.
Florian (npub1gly…x4dg)
