Is urine a barrier that prevents water from reaching the skin during ghusl or wudu’, and must urine be removed before ghusl, and is dried blood on a wound a barrier that prevents water from reaching the skin, and is it permissible to pray with it?

The barrier that prevents the validity of ritual purity (taharah) is anything that has a physical body (jirm) preventing water from reaching the skin. As for something that has no physical body, like urine, it is not considered a barrier, and it is purified by passing water over it. Congealed blood on a wound or elsewhere is considered a barrier that prevents water from reaching the skin, and it must be removed and its place washed, unless the person would be harmed by its removal or by washing it. In that case, they should leave it and wipe over it.