Mudcat pages now specify a codepage, "charset=iso-8859-1", which it did not do formerly. Your Mac tool may correctly deduce that direct input of characters not present in iso-8859-1 is not desired.

Mudcat happens to accept HTML escapes, as used by John above, which is a special feature, so that the Mac cannot be blamed for failing to realise it.

The problems are long known and have been discussed thoroughly.

As you know, Mudcat is about to lose all its charming anachronisms soon, so that all old problems will be replaced by new ones. Until then, enter HTML escapes manually, or use the tool CopyUnicode.