Jan Škoruba yes, tsconfig.json sets declaration to true, but package.json doesn't specify the "types" property, or the more modern and preferred "exports" property. The types are there but package.json doesn't make it public.
Jan Škoruba great! One last detail. Don't think I'm bothering just for the sake of bothering. In "exports", the types always go first. If you were to run the publint package on your newly created package, you'll see the warning about this and the reason behind it. Other than that, I'd say well done.