I've changed src to support high item id, but for this need to update server side to support 2018-11+ clients or 2019-01+ (I don't remember, need to check it).
Until Rathena updates the server side to support the 2019 client, high IDs will not work in the game, because old clients can read only 65k ids from iteminfo and high items showed as "Apple" -unknown item.