All churches have man-made features. If we did everything exactly as in New Testament times, we would all be worshiping in homes and caves, men and women would be kept separate, and the ministers would be unpaid, and probably a thousand other differences.
All seven of the Catholic sacraments can be found in the New Testament: Baptism, Confirmation, Eucharist, Holy Matrimony, Holy Orders, Confession, and Anointing of the sick, although they are called by different names in the Bible. The names we use today are modern names for old rites, but they are all in the bible, nothing “man made” about it.
Catholic holidays (feast days) are days we celebrate the memory a particular event in the life of Jesus or Mary, such as the Feast of the Annunciation, Easter, Nativity of our Lord - (Christmas) etc. There are also feasts for heroic saints and martyrs of the Church. These holidays aren’t in the bible, true, but neither is Labor Day, Fourth of July, Cinco de Mayo and the Superbowl but we all celebrate those don’t we?
Moving the Sabbath to Sunday was a no-brainer for the early church. It’s the Lord’s Day. The Day He rose from the dead. Why on earth would a Christian NOT want to celebrate that day? The Saturday Sabbath was part of the old covenant of Abraham and Moses, which Christians are no longer under, along with circumcision.
Peter was given the Keys to the Kingdom of Heaven and the authority of “binding and loosing” as well as charge over the Lord’s flock, so yes, the Pope, because of his succession from Peter can dictate our cultural practices and doctrines in the Church.
I hope this helps. I’m not an expert on these subjects. Perhaps someone else can explain further. Just curious - are you atheist or leaning towards Catholic or something else? I can’t quite tell.

Peace!